Hi Heidi,
Happy to help!
Here's a quick recording that I made which shows how you can use the crop feature on videos, as well as use it as a reference so you can see how the functionality behaves on my end.
If the cropping feature doesn't work as it does in my video, try repairing your Storyline 360 installation to see if this fixes the issue. You'll also want to make sure that you're working locally when editing your videos to ensure that the changes are saved.
If the issue persists, please open a case with our support team here to reach out to our Support Engineers!