Hi,
Is the app installed? You can check by going to Settings > Apps > Installed apps. If you find it there, uninstall it.
If it isn't installed, the popups may be coming from your browser or ads from a third-party app or website. Let's first check whether browser notifications are causing the issue.
If you're using Microsoft Edge, go to Settings > Privacy, search, and services > Site permissions > All permissions > Notifications. Under Allowed to send notifications, look for any unfamiliar websites, click the three-dot menu next to each one, and select Block or Remove.