If it’s an app that works based on code in your theme, you can comment out that code.
If it’s an app that injects code into theme via content_for_header, you can use some liquid code to identify the url and assign a new content_for_header with the app script removed.
If you’re not comfortable working in the code, you can either hire a Shopify developer or contact the app developers to ask if they can give detailed instructions how to temporarily disable the app.