Presumably this Form 1099-R has code G in box 7. If box 5 of the Form 1099-R is zero or blank, this From 1099-R is reporting a rollover to a traditional IRA, not to a Roth IRA. The fact that the payer refuses to change the Form 1099-R seems to imply that you asked for a rollover to a traditional IRA, not to a Roth IRA, and somehow you diverted the rollover to a Roth IRA.
Assuming that box 5 is blank, you can get TurboTax to treat this as taxable by entering a zero in box 5 and telling TurboTax that this was a rollover to a Roth IRA. However, this might result in the IRS questioning this rollover. A more proper resolution would be to file a substitute Form 1099-R (Form 4852) with the same amount in box 2a as is in box 1 and providing explanation as to why the taxable amount in box 2a is incorrect. Filing Form 4852 will require printing and mailing your tax return; a tax return containing Form 5852 cannot be e-filed with TurboTax.
