How do you fix a rocker arm if it is loose or broken in your car?

Your best bet is to buy the manual. There are multiple ways of adjusting rockers and it depends on the vehicle. Your loose rocker arm may also be an indication of a bent push rod, bent valve, or worn out cam.

there are 2 types of rocker arm studs pressed in and threaded in. if it is pressed i suggest buying the same size threaded stud, tapping the hole and using 2 stacked nuts screw it into the hole in the head. if its threaded just remove the old one and thread in the new one, be sure to check torque value for this application

answer if a rocker arm is broken, u need to remove rocker cover the rocker arms are all on one tube bolted to the head remove the nuts that secure this tube slide as many rocker arms as need to get to broken rocker arm, off the tube replace with new rocker arm replace others that u needed to remove. sit tube with rocker arms back in place making sure that u align all rocker arms to the proper place tighten securing nuts to proper torque over tightening will break the studs then adjust rockers to specs if engine has hydraulic lifters you will not have to adjust replace rocker covers using new gaskets if the rocker ram is loose, adjust to specs if engine has hydraulic ligters, torque to specs job is done