In most cases installment agreements can be updated to include tax owed from a more current year. The IRS can allow you to add the new tax balance into the existing payment plan. In fact, the IRS does not allow you to have more than one payment agreement, so to include the current year taxes due, you would need to modify the current agreement. It is important to address this ASAP as you could be in default of your current agrement by not staying current on your furture tax obligations (including the new taxes due for the current year).
There are a couple ways to modify your current agreement:
1. The IRS Online Payment Agreement Tool: https://www.irs.gov/newsroom/irs-self-service-payment-plan-options-fast-easy-and-secure
2. By Phone: https://www.irs.gov/payments/payment-plans-installment-agreements#:~:text=If%20you%20are%20unable%20...
3. By Mail: https://www.irs.gov/instructions/i9465
4. In-Person: there are local IRS office that you can make an appointment to visit https://apps.irs.gov/app/office-locator/
As you are now filing separate, but you have a payment plan in place that is joint, it my be beneficial to discuss this with an IRS representative by phone or in-person to figure out how to include these taxes on your separate return to a plan in that past that has included both of you.
