How do i ammend last years tax return with a 1099r form that I can't find or do I even need to since I've already received my refund?

First I would contact the place that issued the 1099R to see if you can get a duplicate one from them, as you need the dollar amounts to file an amended return.

If this is 2016 return and you can't get this from who issued it you try this.

https://www.irs.gov/individuals/tax-return-transcript-types-and-ways-to-order-them

order a:  Wage and Income Transcript - shows data from information returns we receive such as Forms W-2, 1099, 1098 and Form 5498, IRA Contribution Information. Current tax year information may not be complete until July. This transcript is available for up to 10 prior years using Get Transcript Online or Form 4506-T.

Then file an amended return:

https://ttlc.intuit.com/replies/3288565