Mount the TC disk in Finder on your Mac.. select the sparsebundle file you no longer need and trash it.
Post back if you have issues doing this. We need a bit more info about TC and OS on the computer to figure out what went wrong.
Many people post this question and there are lots of more detailed answers if you look.
https://discussions.apple.com/thread/252113492
Note if you have upgraded to Big Sur it is no bad thing to completely erase the TC and start new backups. If you don't want to lose the current backups plug a USB Mac formatted drive into the TC and use archive in airport utility.

Archive Disk and then Erase Disk.. and start fresh backups which will be a lot more reliable. If you need older backup it will be on the archive disk.