Generally, RMDs cannot be converted to a Roth IRA but RMDs were waived in 2020. You must indicate to TurboTax that none of the distribution was RMD. If you already enter the 1099-R as RMD and changing your answer to the RMD question doesn't work then you have to delete and renter the 1099-R form. 

1. Click on "Search" on the top right and type “1099-R”
2. Click on “Jump to 1099-R”
3. Click "Continue" and enter the information from your 1099-R
4. Answer questions until you get to “What Did You Do With The Money” and choose “I moved it to another retirement account”
5. Then choose “I did a combination of rolling over, converting, or cashing out money.” and enter the amount next to "Amount converted to a Roth IRA account"

@Kopitiam 

IRS says:

"You can withdraw all or part of
the assets from a traditional IRA and reinvest them (within
60 days) in a Roth IRA. The amount that you withdraw and
timely contribute (convert) to the Roth IRA is called a conversion
contribution. If properly (and timely) rolled over,
the 10% additional tax on early distributions won’t apply.
However, a part or all of the distribution from your traditional
IRA may be included in gross income and subjected
to ordinary income tax."