I cannot locate where to enter my overpayment for 2017 NYS taxes credited to 2018
You need to go to the Federal Taxes section...that's where it is entered.
(or the Personal taxes section if you are using Online SE or Desktop H&B software)
In the Deductions&Credits section. ("I'll choose what I work on"...don't use the "Guide Me" )
Scroll down to the Estimates and Other Taxes Paid section..
...go in on the "Other Income Taxes " line
look for the "2017 refund applied to 2018 state taxes" line....Start there.