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.

These three possible moves would result in the following three piles:

Your third move must have you taking 4 matches from the 12-match pile and adding them to the 4-match pile. So the piles after the second move must be 4, 8, and 12. The only way we can get from the end of the first move to the end of the second move is to take 6 from 14 and double the 6-match pile.

The answer is to:

1. Take 7 from 11 and double the 7-match pile. (4, 14, 6)
2. Take 6 from 14 and double the 6-match pile. (4, 8, 12)
3. Take 4 from 12 and double the 4-match pile. (8, 8, 8)