How can I resize and rotate an OBJ file for weapon?

Hello. I want to make this weapon the size of a normal gun, but idk how. I have tried resizing the model in blender and then exporting it to an obj file, but the missing texture patterns show up. I want to do something like what blockbench does. Does anybody know a way to convert an obj file to a JSON file in order to use it with blockbench, or resize it to a normal size without breaking everything? It currently looks like this: