Amending 1099-R

Hi everyone, I'm just so stressed about this whole process of amending this 1099-R form. I didn't rollover so I was sent the money. Got the forms late after my return was accepted, so I see how much I need to pay back. My question is do I pay this through the IRS? Can I pay this online? And lastly what will happen if I wanted to wait until next year's return?