Forget anything that's been posted about Sentinel and Favorites Lists. Those apply to "newer" Uniden scanners and you have an older one.
Uniden is a little "goofy" when it comes to priority scanning on trunked systems, which you have there. It does not do a true priority ID scan, as in preempting an on-going transmission to check for a transmission on a higher priority talkgroup.
You mentioned you did not program it. There is a way to do what you want, pretty easily though it isn't the most efficient. But it will require some programing work. Are you able to get that done?
Otherwise, your best bet would be to hit the Hold/Resume button below and to the right of the silver knob. Then, rotate the silver knob until you see MFD 1 or Main (or however it is labeled). Then to resume scanning, hit the hold/resume button again I THINK - possibly you may need to hit the Scan/Search button, been a while since I used my 996XT.
The downside is that if MFD has a structure fire (can't remember if they call it First Alarm or Full Assignment) they'll send responding companies to Tac 3. To hear that channel, you'll have to rotate that knob some more. You'll know if its a structure because they send about 3 chief officers.
Also if when in hold and rotating silver knob, you start seeing numbers like 851, 852, 853, you've gone too far - scroll back the other way or hit Hold/Resume to get back scanning. Then try again.
You are on a trunked system, Minnesota ARMER. Site 109 is also known as Minneapolis NS. It is the site that all Minneapolis talkgroups are usually carried on. The ARMER system is a great system, but is very complex.