Can not attach Extender to AC2000 Cable Modem router

Had it working great then an electric cut the Suddenlink line for a day and I can not get it going again.

Working to connect a range extender to the Cable Model listed above. I see it has the wrong MAC address listed for modem yet not sure where to change only that address. Have a information in a Word format on the attached file. It is an Appple iMac.

Modem is AC1750 Cable Modem Router model C6300v2. Extender. NIghthawk X4 AC2200 Model EX7300v2.