what is the best way to build power in my legs

Hello Debbie Collins,
The best way is to work with a trainer to handle any imbalance and/or contraindication. Then you will want to incorporate cross training to hit your musculature from all angles. The rower requires upper body and core strength as well.
Make sure you eat well, hydrate and sleep well to round out your strength gains.
Thank you,
Natalie aka NAPS 2 B Fit.