Look at this drawing. Your looking for 10 and 26. You need to find what that link is hooked to. Either a solenoid that is keeping it polled closed or a leaver that hooks to it to open and close. Not being familiar with your motor I’m not sure how the choke is activated. If it is in the twist grip something could have come loose.
Mercury Outboard Parts by Year (Mercury, Mariner, Mark, Force, Chrysler, Sears, SportJet) Mercury Outboard OEM Parts Diagram for CARBURETOR(SEAPRO/MARATHON 15/25 & SUPER 15) | Boats.net