When you uninstall an app it no longer has access scopes to your shop. This happens immediately. However some apps modify the theme code so when they are removed their mods still remain. A quick search for that app you're talking about brings me this page. Perhaps it will help, though ping the app devs if there's concerns.
I am really sorry for the delay in responding - we have only just seen a number of mentions on the form, going forwards we will get a notification for forum posts and respond much quicker.
Thank you, @Jason, for jumping in for us and providing the guide to uninstall. @Chuelchie hopefully, you found the app that as perfect for your business? If not maybe you would like to take another look at the Store Pickup + Delivery app, we have a range of new features and the support team is bigger stronger than ever before - we would be glad to welcome you back and get you set up. We now offer professional set up sessions for free to make adding our app as easy as possible.
If you need any more assistance or information you can email us at firstname.lastname@example.org, you can also start a live chat via the Support tab in the Store Pickup + Delivery app or by visiting www.zapiet.com.