If its through xfinity, you could factory reset it and simply follow the install guide and activation. Or you could call xfinity (after connecting it) and have them provision it.
https://content.abt.com/documents/107084/SBG8300_quick_start.pdf
Hi @alamonica. I have experience moving from an apartment to a house with SURFboard modem SB8200 on Xfinity service. I was able to connect my SB8200 and use Xfinity mobile app to activate the modem. It took over an hour to get online.
Make sure Xfinity service is activate at your new apartment, connect your SBG8300 to the coaxial line, and activate with Xfinity app. Even try calling Xfinity if their service is available in your unit. You should factory reset the SBG8300 as the last resort. Good luck!