How can I uninstall an app from my iPhone?

What app is this? If this is a native Apple app that came pre-installed onto your iPhone, you may not be able to delete it. If not, you may have Screen Time restrictions enabled preventing you from deleting it. Go to Settings > Screen Time > Content and Privacy Restrictions > iTunes and App Store Purchases > Deleting Apps > Turn on. Or if this iPhone is managed by your school or work, you may not be able to delete apps due to their mobile device management restrictions.

Here are the built-in apps that can be deleted, and those that cannot:

Delete built-in Apple apps from your iPhone, iPad, or Apple Watch - Apple Support

If that does not describe the app involved, then shut off Screen Time / Parental Controls / Focus, and check again.