Make ASP.NET application use MYSQL database instead of JSON file

I have an ASP.NET application which currently uses a JSON file as its database. We are moving the database to MYSQL. Below I have included the diagram which indicates the database's structure along with the script that was used to create it. Upon selection to complete this job, I will share my private Github repository with you and you will receive the credentials to access the database. I do not have strict requirements for what framework(s) should be used to access the database. I just want something that my team will find easy to use by example. I came across a Nuget package https://www.nuget.org/packages/linq2db.MySql/ which seemed like a nice way to access the database but feel free to use whatever you are comfortable with. In addition, I want to make it so the /admin/ folder can only be accessed by our website's admin. This can be done just by having it check a fixed cookie which we can manually give the admin's browser. Please let me know of any questions.