You must not change the taxable amount in box 2a. The amount in box 2a of a Form 1099-R reporting a regular distribution from a traditional IRA, including a distribution that is rolled over, is required to have the same amount in box 2a as is in box 1. It's reporting that distribution as having been moved to another retirement account that makes the distribution nontaxable.
If TurboTax asks, you must indicate that none of the distribution was RMD. If you previously answered this question by indicating that some or all of the distribution was RMD, delete the 1099-R form from TurboTax and reenter it. Then indicate that you moved the money to another retirement account or returned it to the same account, then indicate the amount rolled over.
