Hi,

Yes, you can give class 12 boards but you have to study again.

The basic eligibility criteria for admission in class 12 is -

(i) No admission shall be taken in Class XII directly. Provided further that admission to Class XII in a school shall be open only to such a student who: has completed a regular course of study for class XI and. has passed Class XI examination from a school affiliated to this Board.

You can get either a transfer certificate and take admission in some other schools or you want to continue the education in same school contact the concerned authorities and show all the health certificate to prove you request. You have to take again admission to class 12th and need to consult with the school authority, however you have to produce the medical certificate and 11th marksheet to take admission in 12th course.  generally you will not allow for board exam if you did not have the minimum attendance.

I suggest you to directly contact with school admission cell to know about details of  admission.

Hope this helps.

Good luck.