Remount and resolder the upper PCB then connect your mouse to the computer and check that it still functions.

Tip: You don't need to reassemble the entire mouse to ensure that the new Omron switch is working. Just connect the USB cable and try clicking with the replaced switch!

Once reassembled, test further before adding the skates/feet.

Once everything is confirmed working, reassemble and reconnect everything you took out and you'll have a working mouse again! :D