Where do i report 403b contibution?

They are already reported on your W-2 in box 12 with a code of E.  They are not entered anywhere else on your tax return.

Your 403b contribution is reported in box 12 of your W-2 with the letter code E or BB. Therefore, all you need to do is enter your W-2.

1. Click on "Search" on the top right and type “W-2” 
2. Click on “Jump to W-2”