I use "erase Eeprom" sample program in the Eprom folder of ArduinoIDE.
Also don't forget to send "M502 & M500 " after you reflashed firmware to make marlin read the new parameters ( M502 ) and store them to Eeprom ( M500 )
Also don't forget to send "M502 & M500 " after you reflashed firmware to make marlin read the new parameters ( M502 ) and store them to Eeprom ( M500 )