>>7808157on a basic level
copy paste your clip and line up like this. move the start of one over the end of the other until they line up close enough lower opacity of copy like I have here. Test and keep moving along again if not perfect.
If your clip doesn't have a good loop region within you're going to need to learn some more advanced video editing techniques to force the end to line up with the start.
after all that just trim the ending of your first clip to match where the best ending spot was and render that out for a perfect looping clip.
hopefully that gives some direction. anything more go to reddit like
>>7808174 said or learn the basics of whatever editor you're using and it'll come to you. YouTube is your friend as well.