Simple desktop app based on partially written code

I need to write a simple desktop app based on a code which is already partially written, (only minor graphic enhancemnt to be made). The code is already present as web app on our website.

We are using as of now, Firebase for logins and database, open to suggestion for more userfirendly and straightforward alternatives.

Please apply to see the webb app as it is now and with a way and costs for the login and database process.