12.5 Ambient Temperature correction (input actual ambient temperature) {DMM cold junction temp}
Function switch in Temperature.
LCD display default value of 25C or the last adjustment of the ambient temperature (non-current temperature) according to the environment at the time of calibration.
Temperature, press +/- to adjust to the ambient temperature (adjustable range 0 ~ 50C).
Note: If you do not adjust the LCD and the default display temperature is the current ambient temperature, at this time need to press at least +/-
The whole time, if the previous adjustment does not need to adjust again, press SELECT skip.

According to the very limited information I could find in the original Chinese manual, the display of an “Err” (followed by a number 0~4) indicates something is wrong with the measurement circuitry. However the manual did not explain much but did suggest that it could be a fault in one of the voltage dividers. Unfortunately, that’s all the information I could find.

Err3 The present measurement range and the range of the stored reading is not the samewhen recalling the reading

12.5 Ambient temperature correction (input actual ambient temperature)
The measurement function of the meter to be calibrated is placed in the temperature file (or resistance file (J1A, J1B short circuit)).
The LCD displays the default value of 25°C or the ambient temperature at the time of the last adjustment (not the current temperature). According to the environment at the time of calibration
For temperature, press +/ to adjust the display to ambient temperature (adjustable range 0~50℃).
Note•If it has not been adjusted and the temperature displayed on the LCD by default is the current ambient temperature, at least press +/one to adjust
It is exactly once, if there has been adjustment before, there is no need to adjust again, press SELECT to skip.

1-Simply hold pressed the HOLD+SELECT buttons while you turn on the meter to the ohms/continuity/diode option (second position). Then release the buttons.
I am not sure if this wheel position is really mandatory, but it is described in some places as the correct method.
The meter will show "CAL" and will do some auto tests. You can abort this tests pressing select 2 times. If you let it run over, it will end the auto-tests after some minutes.
(note: after change the count config to reach 6200 counts the aut-test take much more time, then I gave up waiting).

2-Now put in the function/scale you want to calibrate (rotate the wheel and press select until you reach there), can be DCV for example.
I tested only for DCV (all ranges) and DCA (all ranges) but most probably it will work for others, like ohms and capacitance. The ACV seams to share the calibration of DCV. I did not tested ACA.

3- Now comes the main part (apparently undocumented). While you are in whatever function you chose before, you can calibrate the zero point by pressing the ZERO button (once per function/scale calibration procedure) and the gain by pressing the HOLD button (short press to decrease the reading and long press to increase the reading). However, to do so you need to feed the leads with a known integer value, once each press in HOLD will jump the reading to next integer above(long press) or below(short press). So, for example if you feed 12.00Vdc but you read 11.82Vdc, than long press HOLD while you are sure the correct voltage is 12.00Vdc and the meter will adjust the reading to 12.00Vdc (first integer above 11.8V).
-Therefore, each long press will jump the reading to next integer above, while the short press will make jump to the next integer below.
-Depending the scale you are the jump may not be an integer, however you will figure it out while doing the process.
-Pay attention to the scale you are. As DCV is autoscale you need to adjust when you are at 0.000, when you are 00.00 and when you are 000.0. You need to change the scale by changing your voltage source. The point in each range to calibrate is a personal choice. I noticed that the linearity is not so good, than I prefered to calibrate at 17.00Vdc the 60Vdc range once I will be reading values mainly from my battery bank between 12 and 24Vdc.

4-After the procedure for all functions and scales you are interested to calibrate just turn off the meter. In the next turn on the new calibration is used normally.

To enter the normal calibration mode, you need to close S1 (according to the J8 scheme) and turn on the multimeter. Tests of something internal will begin, after the tests are completed, the calibration mode should turn on directly. After passing the tests, I get the message Err0. Something is not right, but what exactly the hell you understand.
If you immediately switch the selector to either Ω or Hz, then the tests will pass without errors.