Hi

If you don't have details related to your 11th class then skip filling it. Just fill basic details like college name or college board or year of passing if you don't have even that then skip that too. You can still fill the form and submit it.

make sure to fill other details properly as there is no other chance to recorrect it later. Make sure to keep extra copies of your admit card and application form with you as students had faced issues in the past because of this. Wait for any updates from NEET as this has been a huge problem this year with many students so probably they will come up with something soon ,you have time till October 10th but don't delay too much.

Hope this helped!