I forgot to mail my t2202a for last years tax return when I received a Processing Review letter from the CRA in August,what should I do now since I'm passed the deadline?

I was able to send it electronically CRA site the letter provided

If you still have last year's T2202A, fax a copy of it, and a copy of the letter requesting the information to the fax number on the letter.  Put the reference number from the letter at the top of the T2202A.

I have another question if you don't mind. For doing this years tax return should I tick the empty box for "Unused tuition fees and education amounts from previous years" for online tax return or the box for "Tuition fees on a receipt, T2202A, or TL11" or both? or am I supposed to do something else?

No, because it will presumably be used in the reassessment when you send in the T1. You should be fine with just the T1 adjustment.