Unable to update android version

I have a Samsung Galaxy s7 edge that is working totally fine, but it is stuck on the initial android 6 release that comes with the phone. Apparently, the phone can be updated to android 8, but when checking for updates, it says "no update is available for your device at this time. Please try again in 24 hours." I've tried using Samsung Smart Switch on the computer with the phone connected, only to get a similar result. Is there any way I can make the phone download the latest supported update without rooting it? Its an AT&T variant s7 edge. Any advice would be appreciated!