How to remove stuck ear pad cushion plastic

I decided to replace my old nasty ear pads and when removing them the plastic connecting the ear pads to the housing is stuck on and broken all around. How do I get it off? Would it be safe to try and heat the adhesive with a heat gun/ hair dryer? It is stuck like this in both sides

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I used the heatgun for a little and used the usb cover to pry the plastic up enough to slide a separator between and remove the piece.

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