See https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-2021-return/L1gEU4G3X_US_en_US
If you need to amend multiple past year returns, you might be better off consulting a local tax professional.
https://taxexperts.naea.org/listing/service/individual-tax-preparation
maybe you made the same simple error on past returns and you know what to do.
You can amend three years back, by Tax Day.
The deadline for 2018 has therefore passed.