in my 2019 return, I incorrectly calculated the value of my apartment as I used a wrong FX rate. Would it be OK to state the correct value of the apartment in my 2020 return for calculating the depreciation section in TurboTax
No, don't change your depreciation basis on your 2020 income tax return. You should amend your 2019 income tax return to correctly reflect your depreciation basis at the time you made your apartment available for rent. The depreciation basis may affect your bottom line (your 2019 refund or amount due).
See How do I amend my 2019 TurboTax Online return?
Generally, Form 1040-X, Amended U.S. Individual Income Tax Return, must be filed within three years of the date the original return was filed, or within two years of the date the tax was paid, whichever is later.