Just complete and file the 2020 tax return. If you are not a dependent and you are otherwise eligible you will receive the Recovery Rebate Credit on the federal tax return, Form 1040 Line 30.
The TurboTax program will ask you about any stimulus payment received in 2020 after you have completed the Other Tax Situations section.
Even if you were a dependent, in 2019, you can still get the recovery rebate credit , as long as you do not qualify as a dependent for 2020.
See full dependent rules at: https://turbotax.intuit.com/tax-tools/tax-tips/Family/Rules-for-Claiming-a-Dependent-on-Your-Tax-Ret...