Hi,
You can claim EI overpayment by entering the overpayment amount on T1 general Line 450.
You can switch to Forms mode (by clicking on the Forms icon at the top right end of the toolbar). Then you can open T1 general form. Scroll down to 450 Line and enter the amount.
There are conditions as to what you should be entering as the amount which you can read through at - http://www.cra-arc.gc.ca/tx/ndvdls/tpcs/ncm-tx/rtrn/cmpltng/ddctns/lns409-485/450-eng.html
Hope this helps!
