Is there a way to get rid of the notification that battery is not genuine

The only way to completely get rid of the notification is to get a genuine battery. I believer the badge (the little red number) will eventually go away. However, you always see the message under Settings>Battery as long as you have a non-genuine battery.

The only way to get rid of it at this point is to recycle the phone and go buy one that hasn’t been tampered with.

In addition to the message about a non-genuine Apple battery, the settings for Battery Health / Maximum Capacity will usually not work when the wrong battery has been installed.

You can check this as follows:

Tap Settings

Scroll down and tap Battery

Tap Battery Health > Maximum Capacity

What information appears here?

To get things working correctly again, you need to get a genuine battery installed at either the Apple Store or an authorized Apple Service shop. No one else has access to genuine batteries from Apple.

In the past, Apple has refused to work on phones that have been worked on previously by unauthorized technicians. You should probably ask Apple directly, though, if they will replace the battery in your case.

Or just live with the error message. It won’t interfere with the use of your phone.

The frustrating part is they told me it was a genuine apple and they were authorized repairmen.

Then, take the phone back and have the correct part installed. Don't let the shop off the hook. Either you got a "knock off" battery or the installation was not done correctly.

If the shop really was "Apple authorized", you will be getting a follow up survey from Apple asking about the service that you received. Apple needs your honest answers to help improve service. If you don't get a follow up survey, the shop was not really "authorized" for Apple. It's that simple.