how to convert a .mp4 file to .mov?

Open the .mp4 with Quicktime.

From the menu bar, File > Export > 480p (for example)

The saved film will be in .mov format.

Alternatively, I've found you can just modify the extension of the mp4 file to .mov. To my knowledge, both containers use the same codec, so they are really interchangable.

There are several converters out there. Find one you like and go for it. Only download from trusted sources.

You're welcome. Cheers.