How can I go back to the previous level that I missed?
Could you explain which level you wish to go back to and why.
Your ZCA activity shows some very odd numbers. You are at level 20 with only 479 miles ridden when I would expect around 1600- 2000 miles for level 20.
Do you cycle every day or only once in a while?
Are you cycling without any internet connection - Do you see other riders when you are riding?
I notice on one particular day, 8th August 2021, you went from level 12 to level 18 on one short ride - is this the issue you are trying to correct ?
If so this might be something you need to contact Zwift Support to help you with.