how do I not declare a child as a dependent in pro series basic

If the kid actually provided more than half of his own support, then delete him on the parent's return.

You would determine if the person is not a dependent in 2020. That doesn't mean "not being claimed." It means "no longer qualifies as a dependent." You must correctly address whether they Can be Claimed as a dependent on someone else’s tax return.

You might want to bookmark this link and read the IRS guidance.

Interactive wizards portal includes one for determining dependency:

https://www.irs.gov/help/ita

Why would you want to do that?

In ProSeries Professional you can use Code Q to skip the dependent this year if you don't want to delete the kid's data completely.  Like, when IRS wants him to pay back the $1,800 and the parents figure they might as well get $500 plus tuition credit for him.  

I'm beginning to wonder if IRS is holding back the $1,400 EIP's for parents, based on 2019 returns, when they already have 2020 returns from the kids that claim themselves.