From everything I can find it looks like that app has gone completely belly up, also from 2hat I've read buds was affiliated with it, but buds was not the developer that gets contracted out, since the app is no longer available and the dev isn't listed anywhere I could find you've likely lost that info, even if you could find the dev contact its not likely they'd have records from a dead app.

sorry about loosing the app I keep track of guns s/n using a excel spread sheet that I put together

Not sure if this is the same app, but if it is maybe you could recover your info by downloading to your pc
https://en.freedownloadmanager.org/Windows-PC/MyGunDB.html

Not trying to be smart or anything, but with Google and Big Tech tracking every thing you do and say, my smart phone would be the last place I'd keep data on all my guns, especially on an app downloaded from Apple or Google. You are creating your own registry for Big Tech to turn over to the government.

Joseph, not that I am aware of. I would try contacting the App Vendor and see if they can give you some guidance. Cheers and stay safe!