What you’re looking for is how to rotate your character so that his feet are facing the center of the planet I assume. I already tried that and what you need to do is to literaly set your character’s rotation to something (not add rotation), but that “something” is the experimenting part.
I’m not exactly sure, how is a vector translated into rotation (using the GetRotationFromXVector I think) bout what you can do is some debugging. For example: subtract your player’s position from the plane’t center and you’ll get a vector.
To get only it’s direction you have to Normalize it (with a function) and then try translation that into a rotator and see what happens in different cases.
If you notice, that your character is always facing in a certain direction relative to your planet’s surface then try changing your character’s relative rotation to a certain point, where it will always fix the rotation no matter where on the planet he is.
This is just an idea for making this kind of mechanic. I hope my answer helps you, if you have questions, post them in the comments.