The screw stripped the thread off the arm of the bike the pedal is attached to?

Now the screw won't secure onto the arm of the bike because the hole in the arm is too big with out the metal thread. I need to reattach the pedal, but how? Will glue work? The screw is attached to the pedal in such a way that I can't isolate the screw from the rest of the pedal and the pedal is made from plastic so there is probably no way I can weld it. Also this is a stationary bike.

Go to an autoparts store..and see if they have a product called Fas-Weld. It's a two part putty stick that..when kneaded together like clay...you put the kneaded putty on whatever you are fixing..and it will hold very well.
It's a very hard substance when it's fully cured..and it can be drilled or tapped if you need it to.

I recently saw a product in an auto-parts store (possibly in a hardware store as well) that is a thread restorer. It was in a tube/injector and was some kind of epoxy. Just inject it into the stripped out hole and install the pedal and support it somehow until the compound dries. It will harden as tough as metal. JB weld is also an epoxy putty mix that will permanently glue the pedal to the metal. (sorry about the pun). Good luck.

Well you have a 3 options (none of which will be easy)

(hardest to easiest)

(1) Drill a hole in the pedal part that screws into the arm in the center and tap the hole to make it threaded and then use a wide head bolt with washer to screw into on the other side of the arm. (most-likely out of your ability, requires many tools)

(2) replace ARM from manufacturer, but may take time finding this, and a while to wait on it.

(3) tricky but worth the try, I assume some of the thread is their ,its just shot... Find you some soft tin metal (aluminum can might work). cut it into 2 thin strips and put both strips through the arm hole (1 on top and 1 onthe bottom), now try to force the threaded pedal into the hole of the arm{you may need to bow the metal strips to the roundness of the hole}. use a wrench to force the threading into the arm. the extra metal should hold and it should be permanent, at least until you can replace the arm, but it could hold forever too.. Make sure you cut the left over metal off and bend any edges down as not to cut you in the future.

**Note about the guys above on JB weld compond. They are right that it exists, but unfortuanly, it wont work for your application. a pedal is pushed down and up and forward and reverse as you pedal, it will crack up and falloff after 1 minute of usuage. jb weld holds stuff together better then glue but not a moving part with pressure at the glue point in multple pressure directions.