Pushing down the release bar should depress two hydraulic release pins. They need to be completely compressed to release, sometimes you need to rock the machine back and forth a bit to release the pressure. Be sure to clean that area well before pushing that down, they're been known to stick down and not pop back up if fouled with dirt or rust.
I find many that are stuck in the released position after an owner parked it and let it sit for years, worst case is you remove the valve and free up the pin maybe changing a few orings.
The 916 and 7116 is by far my favorite in those models, the K381 and the earlier Briggs Iron block 16hp int he Simplicity models were pretty much indestructible. Any of the iron single cylinder motors were. I have a 916 myself which I converted to a Briggs motor, I bought it from a dealer who had taken out the Kohler to fix another machine and I was able to buy the rolling tractor minus the engine for $400. Its been my trailer mover now for over 30 years.