How do I change Mirror Modifiers into objects?

Is there a way to make a mirror modifier into an independant object or the entire mesh, which are currently many separate objects into one whole mesh?
I have a mesh arm that I created with a mirror modifier of it on the other side. I’m having Weight Painting issues with the second animated arm, probably because the arm is just a mirror modifier of the other. A little help would be greatly appreciated!

Just click the Apply button on the modifier.