[catch22]

I enthusiastically imported a csv file and the matching pdf, or so I thought, but apparently it is messed up.
For instance the title All of Me opens the file of another tune called Always There.
Beautiful Love opens Birdfood. 

I guess there's no way of somehow undoing the import other then manually checking every single file to delete the corrupted matches? 

[Geoff Bacon]

You can show the filters and type the name of the csv into the search field.
This will display all the entries associated with the CSV,

Long press one of the entries until it has a check mark
Select all the entries (floating dialog at bottom right on Android)

Overflow menu (3 vertical dots, top right)
Create a (temporary) collection from Songs.

You now have a collection of all the songs.
Check that it contains what you think it should and/or identify how the csv needs to be modified

Display the Songs tab (you can't delete songs directly from the collection tab)
Type the name of the temporary collection into the Collection Filter
Long Press to select one of the songs
Select all the songs in the collection (as above)
Delete

Collections Tab
Select the name of the temporary collection and delete

Some add a field for a collection (or setlist) name into the csv file; this saves having to form a temporary collection to clean it up for a retry.

Geoff
Note: It is a good idea to get into the habit of using MS to make a backup before making major changes - this gives you a fallback to a known position should the need arise

[itsme]

Go to the "Songs" tab, filter for the newly imported PDF and delete all the songs. If you haven't set a common field like album or collection for the PDF (which is generally a good idea for batch importing) you can filter for the filename.
The issue is probably caused by the fact that the pages in the CSV don't match the PDF. Alas it's not possible for copyright reasons to share a matching PDF together with the CSV.