MU must show the quality of their own game to the maximum. play well and get the win. No need to think too much about the results from Munich. the most important thing is that they have to win first, and hope that there is still a chance to qualify.
but I have a feeling that this will be quite difficult for MU, they may have to fight again for the Europa League if they are eliminated from the Champions League. currently the biggest possibility that Ten Hag and his team can have is that. It's not that there's no chance, but I think the best possibility for MU is the Europa League.
You seems to be really sure if Manchester United at least will be in the top 3, don't underestimate Copenhagen since they can still able to compete against Galatasaray while Manchester United can't. There's a possibility Manchester United would be in the bottom and not enter Europa league.
Manchester United is really struggle due to lack of good player, so it's not something could be easily solved.