Hi, @Alvin--R !
Katy here from Shopify. I hope all is well with you!
When removing the code from any third party apps, really the best way to do so is by reaching out to the app developer directly. As they have built out the app, they can remove any code injected to your theme with ease.
First, you will need to remove the app (if you have not done so already) This can be done within the Apps section of your admin, by clicking the trashcan icon:
Once you have done so, you can then reach out to the app developer via email to help then remove any residual code which may be present. You can find all of their details via their app profile here too.
If you feel that are unable to reach them, or need a hand with this in any way, do let me know and I can help out!