You have three possible starting moves:

1. Take 7 from 11 and double the 7-match pile, or
2. Take 6 from 11 and double the 6-match pile, or
3. Take 6 from 7 and double the 6-match pile.

Your third move will have to be taking 4 matches from the 12-match pile and adding them to the 4-match pile. This move will create two 8-match piles, so the untouched pile would need to have 8 matches already.