So I started making a repport from an excel file. To begin with it was just for testing so I just typed in a whole lot of data that I got from different places. All in all I have 10 tables in one sheet and it looks really messy.
Now I'm trying to clean up the tables by grouping them on different sheets and changing their name so it's easier to understand what the numbers mean. When I do that I can't seem to refresh my PBI repport as it tells me "The key didn't match any rows in the table".
Ofc I can start over but I have made quite a lot of new columns and measures and also spent a lot of time on the visuals.
Sounds like some of your issues could be fixed by using the Advanced Editor in Power Query.
If you go your model, and select "Edit Query" on a table and then go to the Advanced Editor, you can manually change the paths, columns, column names and much more. Many things can be done by just adding or changing a few words, and you can always save the original query text somewhere so you "reset" if you mess something up.
It will look different depending on if you're importing tables or sheets or something else, but the basic idea is similar. Of course, the more changes you need to do, the more complicated it might get.
Feel free to share screenshots or explain further if you want some more specific help.