not exactly sure what you're describing.
if you take off the cover the "actuator arm" is the lever on top that the clutch cable attaches to, and that's connected to the swiveling rod that goes through the cover. there's an open space and that holds a pin so the rod and the lever don't pull out the top.
with the cover off, that lever will swing back and forth.
on the engine, there's the gear with a black dowel sticking out. behind that dowel is a single ball bearing. you can pull the dowel out with your fingers, and it can also fall out when you remove the cover. if that fell out while you were installing the chain, the bearing might have come with it and rolled away.
if you pull that cover off, pull that dowel out and make sure the bearing is in there. might be hard to see 'cause it's covered in grease.
when you re-install it, make sure it goes together right. there will be a little bit of tension on the lever when you're pushing it back together and putting the bolts in. make sure the lever is facing back towards the rear of the bike and tighten it up.
after it's all back together, the lever will swing to the left (towards the front of the bike) really easy, that's normal, but when it goes towards the rear, it should stop when it's pointing straight back, more or less parallel with the motor chain.
push it as hard as you can towards the right side of the bike. it takes some force, but when it moves, you'll feel the clutch disengaging. when you let go, it should snap back.
if all that's working, then run the cable through the little lever, make sure the cable housing is seated in the clutch lever on the handlebars and the cable stop that's bolted into the engine.
now push that lever on the engine in about an inch and pull the slack out of the cable and tighten it down.
pull the handlebar lever and the rear wheel should roll free. release, and it should stop the wheel.
if this works, you're ready to ride.
if the wheel still won't turn, find a buddy or a way to prop the rear wheel up, then push the lever on the engine in as far as you can while your buddy tries to spin the wheel.
if the wheel spins, then you need to get the cable tighter by pushing the lever in further and tightening the cable back down.