That thingy above is the counterpart of the magnet, you can see the small set screw with Allen key size 1,5 mm.
It is not feasible to adjust the magnet’s strength (itself), but you can increase/decrease the locking force via this small screw.
You simply adjust this screw’s protruding part to create a small gap.
The wider the gap, the lower the force.
Just caution; the screw has to be secured with thread locking compound of middle strength (Loctite 243 for example). During this adhesives curing time the connection must be closed (=under tension).