This video from My Mate VINCE explains it well, but if you don't have access to YouTube, have bad internet, or just like the text instructions better then keep on reading.
Step 1:
Firstly, grab a butterknife and put it in the part between the Joy Con and the strap near the lock.
Step 2:
Now, take the top part of the butterknife and use it like a lever, with the end side going down until it clicks and you can remove it
Step 3:
Celebrate fixing that stupid mistake!