I forgot to claim $6050 of rollover for 2018. There was no 1099. Can't I just add it in?

[dmertz]

If there was no Form 1099-R issued, are you sure that that this was a distribution and rollover?  If you moved funds by trustee-to-trustee transfer from one traditional IRA to another traditional IRA or form one Roth IRA to another Roth IRA, the transfer is neither a distribution nor a rollover and is not reportable.

If this was not a trustee-to-trustee transfer of an IRA, contact the original custodian or plan administrator to obtain the missing Form 1099-R.