You can pay any tax due directly to the IRS reguardless of when you file. You just enter the tax paid in the "taxed paid" section when you file.
Because amended returns are currently taking up to 6 months to process, interest an penalties will start after April 15, so if you owe additional tax it should be paid prior to Apr. 15 regardless of when you amend.
See this IRS article for how to pay:
https://www.irs.gov/payments
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
