If your handlebar pinch bolt is stuck, there are a couple ways you can get it to loosen up.
First being, if you have your own Allen key that is longer or has a longer handle you can use that will provide more torque and it will pop open.
If you do not have a longer handle Allen key, you can grab your seat post (pole for the seat) and you will notice that both ends are hollow. (unless you have the seat on)
You can grab the seat post and slide the Allen key into the seat post and you can use the seat post as leverage.
The seat post will be used as a "longer handle" for more torque and it will pop open.
If you cannot get it loosened up with both methods, I highly suggest taking it to your local bike shop to get it off. They will be able to get it off for you.
Here's an easy hack to get the handlebar loosened:
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