Hello @basilwort5, I can help you with that!
You can change the color/size and other details of you controllers by selecting the Arm (or any other part you want) from the Module Hierarchy on the left. Then, on the Details panel, scroll down to Default and you’ll find the options under Module Settings. You need to tick Override Color if you want to change the color, but the rest should update normally.
If your model is too small, though, you might want to export it with different settings from Blender or change the import settings scale, since it might give you some issues in the future.
Please let me know if that helps!