An In-plan Roth conversion (In-plan Roth Rollover, code G in box 7 of the Form 1099-R) has nothing to do with Form 8606.
An in-plan Roth rollover is generally a taxable transaction unless it consists entirely of after-tax funds and the Form 1099-R shows the same amount in box 5 as is in box 1. If the Form 1099-R has a nonzero amount in box 2a, you must amend.
