How do I get Google Photos to delete files from the backup after I've deleted them on my phone

I am using a Samsung A33. I have backup turned on in Google Photos (V7.11) and it has duly created a backup of all my photos on Google Drive. I recently deleted a large number of unwanted photo files from my phone, but it seems that Photos does not sync with the backup by also removing them from Google Drive. Can someone tell me how I can make this happen, as these deleted files no longer need to be backed up? (NB, I did not delete the files using Google Photos, but rather by connecting my phone to my PC and deleting the files. Perhaps this was a mistake.)