Easy job Matt.
Where the seatbelt bolts to the floor, you have to push off the plastic cover to access the bolt. I found a smooth nose pair of pliers works good for pushing it off. 17mm socket or box wrench to remove that bolt. Then remove the two phillips head screws that hold the plastic "foot" on. That piece will then pop off the bottom of the "B" pillar.
Now with those items removed you pull down on the "B" pillar trim and tread it off the seatbelt (you'll have to cant the bolt through the wider portion of the opening). Thr trim can now be taken out of the car. The sliding ajustment piece will pop out of the channel it rides in and you can access the loose area you want to tack down.
I used laquer thinner to clean off the old adhesive and leave the aluminum panel clean. Then I used 3M trim adhesive to reattach. I put a thin even film of adhesive on both the aluminum and the back side of the leather, let air dry until just tacky to the touch (about 15-20 minutes). Starting on one side, I pulled the leather out taut and wrapped it around the aluminum, then did the opposing side before doing the top/bottom. Turned out nicely.
I also took time to reattach some of the longer runs along the back of the pillar.
The 560 is coming along nicely. Have had the chance to take her out for a couple small spins. Still have to do the T-chain rails and tensioner, tires, and pull/reinstalled the new center console (while cleaning the back seat carpet, found I got the console in crooked, something is out of place). Once I get the next bit of work done, than I can get the safety inspection, smog check and get her duely registered.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.