Hi, this asset was placed in service in 2009.  It is a rental property.  From 2009 to 2017, I was doing everything correctly but in 2018, I transferred to using turbotax to do my taxes.  Unfortunately, I entered in the WRONG basis in 2018, 2019, and 2020 thus triggering a WRONG depreciation expense for those three years (too much depreciation for each year).  I discovered it just now.  My confusion is whether I can 

a) Amend those three years and then move forward

b) Do a form 3115 because I messed up for 2 or more years

c) Something I don't know

I will note that I sold this property (well, 1031 exchange) in 2021 so I am wanting to fix this.  I now heard that since I sold it in 2021, I could correct everything for that tax year.  It is so confusing ... just not sure what to do.  

Thank you.