How would I go about paying extra taxes to the IRS so that I can convert that extra tax refund into I-bonds?

I read that I can submit an extra one-time payment to the IRS so that I can receive that amount as a “tax refund” to convert into I-bonds. When I go into the IRS Online payment portal, do I simply select the option to “Pay Estimated Taxes”? Or is there another option that I would select? Thanks in advance for any advice.

Edit: Also would it be possible for me to submit this extra payment in 2022 (before the April 15 deadline), once I have a better idea of what my tax return would look like, so I can calculate exactly how much to pay to hit the $5000 limit?