How to play save slo-mo video at regular speed

I accidentally recorded an interview in Slo-Mo on the iPhone. I want to save it playing back at regular speed for editing in iMovie.

The Slo-mo setting on the iPhone is record at 1080p at 120fps.

The user guide says "When you record a video in Slo-mo mode, your video records as normal and you see the slow-motion effect when you play it back".

If it was recorded 'as normal', I assume there must be a way of saving the file so it always plays at regular speed?

Can anyone help, please?