The middleman in the sandwich lease options

[Antonio Bodley]

How does the middleman (investor) exit out of the sandwich lease option once the investor finds an end buyer to close on the original purchase price between investor and seller? Would the investor have to use an assignment contract between him and new end buyer to collect the mark-up fee aka assignment fee at closing? I'm just curious because the original seller thinks the middleman is going to close on the property after the lease is up between seller and middleman.