This is only possible via the web app (https://sleeper.app), so you must be using a desktop or laptop.
Once you are logged in, please go to the settings tab inside of your league.
Click edit league, then tap commissioner control, and finally tap edit lineups and matchups.
You now have the ability to do a couple of things. You can move players in and out of lineups, and you can do it for specific weeks. You can even assign "custom points" by editing the points next to any team any week. All of this is tracked in your league chat.
When you are done making changes, hit the Recalculate All Matchup Scores for Week button and the records will be recalculated.