It looks like a simple Disk Repair will trim an SSD.
I got a new SSD and so I booted from a tertiary drive to clone my old SSD onto my new SSD. After the clone I ran Repair Disk and noticed at the end of the repair it "trimmed" my SSD. Maybe I just missed this before, but I don't recall seeing this trim line in repair disk before.
So, to force a trim just boot from anoth ...
I got a new SSD and so I booted from a tertiary drive to clone my old SSD onto my new SSD. After the clone I ran Repair Disk and noticed at the end of the repair it "trimmed" my SSD. Maybe I just missed this before, but I don't recall seeing this trim line in repair disk before.
Verify and Repair volume "newsystem" Checking Journaled HFS Plus volume. Checking extents overflow file. Checking catalog file. Checking multi-linked files. Checking catalog hierarchy. Checking extended attributes file. Checking volume bitmap. Checking volume information. Trimming unused blocks. The volume newsystem appears to be OK. Volume repair complete.Updating boot support partitions for the volume as required.