I don’t quite understand what you’re asking, but I noticed you have one object selected in the Outliner and both forearms selected in the Viewport (without having just the one forearm as the Active Object), so maybe what you’re looking to do is separate these into two objects. If you want to make the arms asymmetrical at this stage while keeping the various body parts as separate meshes, you will need to do that anyway.
Have a look at this:
Also, I think FedPete is suggesting to merge all of these pieces together into a single mesh and then do a remesh. Doing that would also work, and then you would use NP5’s suggestion of symmetrized sculpting as needed. The only issue there is that you won’t be able to just drag the pieces around anymore once you do that, so large-scale placement should be confirmed first if you try this approach. Good time for an incremental save too!