Need Advice: Best Way to Increase Offshore Dev Productivity

I am getting moved to manage a different development group. Ths new group off-shored a large chunk of their work a couple of years ago. It has not gone well, and the hope is that I can somehow improve the productivity of the offshore team.

Currently, our projects are Waterfall but the development and testing are Agile.

I've been frantically searching and reading up on the topic and figured I would come here to maybe speed the process up and get some advice from people who have already addressed this issue.