Download plugin file that is required
This file must be extracted into the ...\Steamlibrary\Steamapps\common\assettocorsa\apps\python\
Be very careful you do not have \Steamlibrary\Steamapps\common\assettocorsa\apps\python\racelablib\racelablib
Enable the racelablib in UI Modules
From main game menu, click options and general - > scroll down to UI Modules and enable Racelablib.
Restart game after adding this setting.