How do I update Control Center app on iMac?

What year model is your iMac..?

see > Identify your iMac model - Apple Support

Control Center gets updated with each macOS version.

see > Update macOS on Mac - Apple Support

If your iMac supports a later macOS version, then update to the latest supported macOS version.

If your iMac does not support a later macOS version, then it is a good time to consider a new Mac.

You should provide a screenshot of what you are seeing. Control Center is part of Mac OS for making quick changes to some Settings and that one cannot be updated, but your message may be referring to an app that is completely different than what is provided by Mac OS.

think if you get some popup telling you that control center needs to be updated and it has a link or button that will send you to some page which want your apple account and or creditcard details then you should not give them..

Recognize and avoid social engineering schemes including phishing messages, phony support calls, and other scams - Apple Support

Identify legitimate emails from the App Store or iTunes Store - Apple Support

That advisory smells of yesterday's diapers to me.

I'm liking the issue Rudegar raises. I do not recall ever having macOS recommend an update to a single system function like Control Panel. Those updates get distributed with system upgrades, like 15.6 to 15.6.1.

Some notifications show a web address of the sender. Earlier today, a poster ( here ) showed images of multiple fake virus notifications displaying the address of a web site in India. Not Apple. It also showed in their System Settings > Notifications.

To add to the excellent links Rudegar listed, I offer this user-submitted tip from John Galt:

Stop unwanted Notifications - Apple Community

OK that's what I thought.

To expand on Mac Jim ID's question, you need to show us or tell us exactly what the Control Center complaining about.