How to unscrew HRM Run lid?

Yesterday battery died in my HRM run sensor. To replace the battery I need to unscrew four screws. I found out that I cannot do it - the screws stuck. I managed to remove one of them, but all others are completely stuck and do not move. Unfortunately I damaged heads on those that stuck. I tried WD-40 overnight, but it did not help. How can I remove the screws? Given how much these Garmin sensors cost, I do not want to buy a new one because screws get stuck.

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