HELP! New update deleted all my stuff - HOW DO I GET IT BACK??

Hello,
I was running the app on an iphone, IOS 13.1.3. I noticed the app was lagging and a bit slow at times so I installed the update in the app store. Once I reopened the app ALL my stuff was gone - playlists, personal charts, edits, settings, everything. It was like I had downloaded it for the first time and was reset to the default version.

Do you know why this happened and how I could get my old version back again? This has never happened to me after installing an update. I'll do whatever it takes.

As you could imagine this is beyond stressful as I had spent hours and hours putting work into the app. I'm a professional pianist so naturally I am going to have to use the app again very soon. Thank you so much to anyone who could help!