If I had taxes taken out of my unemployment compensation, but that is not reflected on my 1099-G how should I proceed?

Did you enter the taxes withheld in the section for entering the unemployment compensation?

On the screen What's the total amount you received on your 1099-G? check the box Federal or state income tax was withheld on this payment.

Federal taxes withheld will be entered on Form 1040 Line 25b as a tax payment.

If you had tax withheld from your unemployment but it is not shown on your 1099G you need to sort that out with the unemployment bureau and find out why it is not there.   The 1099G that you have is the same information that the state sent to the IRS so you cannot just alter it on your own.