I am missing a1099R.I feel like I need get an extension. How do I do that?

https://turbotax.intuit.com/irs-tax-extensions/

Turbo tax has a file for extension option.  However, you still have to  pay your taxes by 5/17/2021 in order to avoid penalties.  If you think you owe taxes, then make a payment that is more than what you think you owe.  When you file your taxes you can always get back any extra that you paid.