Here is a tutorial by Justin Brown on how to edit 360 videos on your Android phone with Collect, a free 360 video editing app for Android. (Correction: Justin mentions iOS as well but there’s no iOS version for Collect yet, although it is in the works.)
One thing I like about Collect is that you have the option to turn off the watermark. The other free 360 video editors such as V360 and Veer Editor don’t have that option yet. Collect is available for free download on the Google Play Store.