My First app with database interact

I am creating my first app.

My case is:

I want to create a financial control for festivals.
The user will receive a bracelet at the entrance of the party where there will be a QR Code.
When the user arrives he will be directed to go to the cashier to carry his bracelet with credits to use at the bar and conveniences

It would be 3 steps.
1- The User needs to log into the app to identify which type of function:
-Box -> will recharge the bracelet
-Bar will read the QR code (where you can check the current balance and discount what the customer asks for.

-I need it to work on an offline network between cell phones and a physical server.
-I need to know how to query and add or subtract user values
-I know almost nothing about databases

Could someone help me by giving tips on where to search for the necessary material?
I found a lot of information about firebase and tinyDB but I couldn’t digest it all

Are you expecting someone to hire for this?
Or asking someone to create aia file for you

As the first app, Its a complex app.
Even though some say “it’s easy” I say it’s not. The process of creating a good software / app is long and takes steps. In addition to the app, you need a local server (I think I answered this in the Facebook group).
So tinydb and Sqlite are on the user’s mobile.
Firebase, on the web.
MySQL you need to create a local server.
Here in the community there is a lot of material (if you want to do it yourself) or you can hire someone to make this app.