I have 4 arms and 1 broke how do I fix it?
What did you break?
A propeller or a drone's arm?
For a broken propeller, refer back to your user manual and my previous posts.
For a broken arm, say bye to the drone. If it is just the plastic arm that is broken and not the wiring or the mechanism, you might be able to glue it and duct tap it ( I did it once on one of my Eachine drones). Otherwise, it's history.
Adding : Slightly off-topic.......
Baking soda and crazy glue will bind broken plastic parts securely. I had an Eachine EX2H drone with a broken arm. I "fused" the broken plastic parts together plus duct tape for good measures, and it flew like nothing had happened.