Can I deduct money overpaid to retail clerks union retirement. They reassessed my benefits and had to pay back $2,125.00?

Yes, you can deduct it.  Will it affect your return?  Maybe.

The Claim of Right allows you to take a deduction (or credit) for repayment of income that was taxable in a prior year.  If you don’t itemize, that won't be helpful to you!

IF you pay back less than $3000, the repayments are deductible on Schedule A (subject to the limitation of 2% of your Adjusted Gross Income.)

To report the repayment:

• Log into your return
• Click on Federal
• Click on Deductions and Credits
• Scroll to Other Deductions and Credits. 
• If needed, click on the Show more button.
• Click the button next to Other Deductible Expenses
• The Generation-Skipping tax question doesn't apply to you.
• On the next screen, you will be asked if you have any of the less common expenses.  (One of the expenses listed is the repayment of $3000 or less.)
• On the following screen, you can enter a description and amount.