@moumi32 examples / factory
or examples / arduino / factory
This post has instructions with link to official repository and flashing instructions: https://community.lilygo.cc/post/295
There is also a GMT offset and DST (daylight savings) you can modify in the header file pin_config.h
Look at the timezone functions for esp32 and you'll see you can specify a timezone instead and forget about offsets, but requires changing one line.