[Fixed]-Django How to access another object by having a user name?

You have two foreign keys from CustomUser to Score. The first one, user_from, does not set a related_name, so it uses the default, which is score_set:

x = y.score_set.all()

The second does set a related_name, so you use that:

x = y.user_to.all()

Note that this does not make much sense as a related name, since it points to scores, not users; it should probably be something like scores_to_user.