Just say NO!

thank you, but that is not the right answer. 

if you mean when the question pops up in 2019, you are correct: but it is too late for that.

Then it's too late to stop it.

If you don't want them in 2020 yet you can delete them in the 2020 program. Then re pro forma later when the software is more up to speed.

Go to 2020 and press F3 and select all clients, then press the delete button. If you have a client you want to keep, you can highlight it before hitting delete. 

It is best to wait as long as you can before doing the proforma OR the organizer. 

If you see the question there is also a check box to the effect of "don't bother me again with this question"