There are a few ways. The value of your voltage can be input into the source code and compiled into firmware.
A workaround would be to calibrate the ammeter 5% low using WiFi in developer mode in the RAPI tab. Amps would read a little low but power calculations would be closer.
The latest development firmware has an option to set voltage, but will be lost each reboot. I am planning to validate the firmware and create a release in the next couple weeks.
|SV mv - Set Voltage for power calculations to mv millivolts|
|$SV 223576 - set voltage to 223.576|
|- only available if VOLTMETER not defined and KWH_RECORDING defined|
|- volatile - value is lost, and replaced with VOLTS_FOR_Lx at boot|
The last and most dynamic option uses a live voltage from another source (solar, energy meter, etc) over MQTT and updates the voltage every fer seconds using updated firmware and the command above. For this you need the latest ESP32 WiFi module and code 3.2.0 or later.