Navigate to https://www.last.fm/user/YOUR_USERNAME/library
and find the tracks you want to delete.
Open delete_scrobbles.js
and replace DELETE_MATCHING
with text that is contained in the scrobbles that you want to delete. For example, if you want to delete Radiohead
scrobbles, do the following:
const DELETE_MATCHING = "Radiohead";
Then copy and past the script into your browser's JavaScript console.
Turn this into a UserScript so you don't need to enter it via the JavaScript console.