Can I consolidate 2 TimeMachine files onto one drive ?

I have two hard drives, one is large (5tb) and the other is much smaller (1tb). There's a lot of free space on the large drive and I would like to move the files from the small drive onto the large one if possible. Even as an admin I can't just copy the files.

Details, details: the large drive has TM data for a few months up until about a month ago, but there were a lot of apps (etc) installed on the computer that I didn't want to be restored to a new computer that I was going to get so I initialized the small drive and then told TM to skip the folders of the stuff I didn't want restored - Pro Tools, etc. So, now I had a TM backup that I could use in migrating to a new Mac. TM backed up to the new drive for a few weeks.

After about a month, the new Mac arrived and the migration from TM to the new machine worked just fine.

So far so good ... now I'd like to move the files from the small drive onto the large drive and have TM use that one going forward.

As I said, my account has admin privs but Sonoma won't let me use the finder to copy files from on drive to another. I'm familiar with Unix and Terminal but wanted to ask what all you folks thought.

Thanks, John