Rental depreciation not accurately reflected on my return. How to amend Form 4562? (Was fine for the first 6 years then $0 depreciation even though SL method)

You need to go back and amend the 2020, 2021 & 2022 returns to correct the error. 

You need to amend starting with the oldest first. I think that would be the 2020 tax return.

After you amend the 2020 return make sure you print out "BOTH" 4562's for that rental property, because you will "NEED" them for the 2021 return. When you amend the 2021 return, your changed "prior years depreciation" will have to be changed manually by you, since it's not possible to import from a prior year return when you are amending. Same will hold true for your 2022 return if you need to amend that too.