Sorry you can’t use Turbo Tax to prepare or amend 2020 even if you filed from Turbo Tax. They only support the last 3 years.
Even if you find or reinstall the Desktop program, you will never be able to activate the 2020 program with the License Code. The License Code started in 2019. So it needs to connect to Turbo Tax to verify the License Code. But they have stopped supporting 2020 and prior.
