If you're having trouble recording on your computer, and you can't find a solution after:
You are welcome to email me! However, the easiest option might be just to record on one of your groupmate's laptops instead.
If you're not seeing a drop-down menu for "Record Slide Show" (under the "Slide Show" tab), so you don't see an option to record one slide at a time, these instructions should help (PowerPoint for Mac 2016 recording)
It looks like PowerPoint will automatically keep your recordings with the slide you're on, and you can hide all but one or two slides to record them individually. If you have PowerPoint 2011, it will let you pause recording between slides.
If you're not seeing an option to save your file as MPEG-4, try using File > Export instead of File > Save As.
Per the Microsoft article Record a slide show with narration and slide timings, you can't record narration in online versions of PowerPoint.
Since Chromebooks are fundamentally browser-based, it looks like the best solution will be to use a groupmate's computer.