UFP brand? If so, there's a hole right under the actuator in front of a small tab. Through there a flat head screwdriver can work the piston back and forth. IF it clicks, push up on the tab to release...do this until you feel it stiffin up then let some fluid out at the hub or caliper..FURTHEST one away which should be the left hand side. (port side of boat) Repeat getting all air out of system and have a solid flow of fluid.
Put some fluid in the actuator first, after you install the solenoid, and leave the brake line off...get fluid to come out them put the line back on and do the above instructions.
I may have a link to that manual...I'll post again of I do.