frozen wiper arm problem

This morning I turned on the wipers and the drivers side was frozen to the bottom. Well the drivers side stayed put, and the passenger side went up. Now the drivers side seems loose ( please tell me those don't strip teeth
out ). How do I remove the arm to inspect it and put it back on into the right position? There is a little black cap on top that just spin but looks more like a cover than a screw. This is on a 2001 Chevy 2500HD
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Reset both arms into the home position then pull the black cap off and tighten a 13mm nut under the cap. Recheck the other side for tightness.
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