You would only use Code "G" if the ENTIRE amount in Box 1 was rolled back! And this should already have been reflected on the 1099-R provided by your investment company, if that were the case. If you only rolled back PART of the Box 1 amount, leave the Code as "7" and insure the "Taxable Amount Not Determined" box is checked. (If it isn't, get a corrected form from the investment company to which you made a partial rollback.) Now do the following: On the Form 1040 TurboTax Worksheet (using Forms Method), check that the amount of your PARTIAL rollback is reflected on Line B2 of "Rollovers, Roth Conversions, Roth Rollovers, and Recharacterizations". If the amount you rolled back is not there, then you need to revisit the 1099-R in question and make sure that you answered the question "Was the withdrawal an RMD for 2019" with "Yes, some or all of this withdrawal was an RMD" then go on to answer "Part of this distribution was an RMD" and enter the total RMD Amount by SUBTRACTING the amount of your rollover from the total reflected in Box 1. Later on, check that "I did a combination of rolling over, converting, or cashing out the money" and enter your rollover amount in "Amount rolled over to another (or back to the same) retirement account. Needlessly complicated, indeed!
