Question About Adding To Existing Payment Plan

Hello! I would appreciate some help here and I get it isn't great to be adding to an existing payment plan as it should be paid in full each year. I've been a bit chewed out about this already, I would just love some constructive help if possible thank you!

I owe some, not a lot from 2024 that I already have a payment plan on. I am anticipating I may owe as well some of which I can't pay for 2025, despite estimated payments. If I cannot pay all of it this tax season, what is the process to add it to the previous plan if anyone knows?

Or will I need to set up a whole new plan? And if so should I call now before I have the balance for 2025 or wait for a notice in May as I did last year. Thank you!