ModuleNotFoundError: No module named 'erpnext' | Error: No such command 'start'

after upgrades the python from 3.6 to 3.9 whenever I tried ‘bench start’ or ‘bench restart’ I faced these errors as listed

with errors:
ModuleNotFoundError: No module named ‘erpnext’
Error: No such command ‘start’

as shown in the picture below