If I converted my traditional IRA funds to Roth but forgot to submit it with my tax return, how do I file an amendment to pay those taxes? I only received a Form 5498.

[Critter-3]

If you converted a traditional IRA to a ROTH   a 1099-R should have been issued for the conversion ... talk to the IRA administrator to get the missing form. 

How to Amend

https://ttlc.intuit.com/community/amending/help/how-to-amend-change-or-correct-a-return-you-already-...