You can't delete an app that is in use on Mac. It is easy to fix this issue. You just need to quit the app on Mac first and then try to uninstall it again.
There are multiple ways you can choose to close app on Mac. In case you can quit the app on Mac, you can force quit it via the Apple Menu, force quit keyboard shortcuts, Activity Monitor, and Terminal. Then repeat the steps to uninstall apps from Mac.
If you want to delete the app and all of its files/folders from Mac altogether, the easiest way is using iBoysoft MagicMenu, the right-click tool for Mac, it enables you to remove unwanted apps with all of the related files within one click. Just right-click the unwanted app and choose Uninstall from the Finder context menu.