how to make 30fps footage play as 25fps [slo-mo]?

Hi

We shoot all our projects at 25FPS  - it's a Europe thing. Some students have footage shot at 30FPS because they wanted a minor slow-mo effect. How do we get this footage to play at 25FPS in a 25FPS project?

When we do slo-mo with Go Pro footage we use the Go Pro app to render the footage. I also seem to remember using Apple's Cinema Tools to alter metadata many years ago.....

Thanks for any advice

Nigel