Hello.
Make sure that the power is off.
Your cooktop is held most likely from underneath by couple of screws. Take them out then using potty knife cut the seal around the glass. Pull out the cooktop, turn it so it wouldn't fall into the cut out.
Take out the screws around the perimeter under the top. Take the knobs off careful not to brake the shafts off. Replace the glass top.
Reassemble in the revers order.

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