Setting Wacom ExpressKey to control brush size

Hi, I just switched to Apple and I'm having trouble giving the ExpressKey the ctrl+option function that controls brush size in Photoshop from my Wacom Intuos M tablet. can someone please help me?

I tried in the Wacom Desktop Center program and then in the ExpressKey settings but I cannot assign the keyboard keys to any of the buttons on my tablet.

Thank you 🙏