Want to retrieve data from the app which is no longer available

I suggest that you contact that app's support team, asking them if there's a solution for your problem.

See this:--> How to contact an app developer - Apple Support

Regards

Giulio

Okay, if you know the name of that app, search for it in Internet, and see if they still have a website where asking for support.

Shouldn't be this case, we can't help you any further, sorry.

Giulio