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My excercise goal is set to 30 mins. I don't see any way to increase it.

Any ideas?

You can't. The same way you can't increase the 12 stands goal.
Probably because it's the recommended value for every human and that's the reason to be for these goals. You can adjust your move goal to personalize your activity rings. Just use Force Touch anywhere inside your Activity app on your Apple Watch.
 
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