Problems with deleting files from Time Machine backup

Apologies if this has been answered elsewhere but I can't readily find the answer. I want to delete one large file and some smaller ones that Time Machine has backed up on my iMac. But for some reason, Time Machine won't let me do this. When I enter Time Machine and navigate to the point in time where I want to delete these files, there is no gear icon which allows me to choose "Delete backup". Nor can I find any other way of deleting these files. When I look inside the external drive I use for Time Machine backup, I no longer see the Backups.backups folder. Instead I get a heading that reads "Backups of Max's iMac" and then three folders underneath that which read 2021-09-25-[six figure number]. Maybe I've screwed something up when overhauling my external drive yesterday (ie deleting lots of files in the Backups.backups folder to make room for new files) but I'v done this many times before without any problems. All and any help would be welcome.