VAT refund

Dear all,

I will soon be travelling abroad from Don Mueang Airport.

How should I go about getting my VAT refund?

(I have the forms from the shops, acquired when I bought the things)

Do I check in first?

Where is the VAT refund desk? Before or after security?

Do I need to travel with the bought item and show them?

Do I need to bring them in the original boxes? (which could be difficult to travel with as carry-on-luggage, hence the question of checking in and the location of the check in counter)

Thank you for your help!