This is what i did in mit app invertor for the log in sign up page. Now, how i can add blocks that check if the username already exists so that the user should use another username?

Viewer when Log_in Click do call FirebaseDB1 when Sign up Click do call FirebaseDB1- StoreValue tag valueToStore a Text GetValue TextBox1 Text TextBox1 Text PasswordTextBox1 tag valuelfTagNot There NA when FirebaseDB1 GotValue when Start Click tag value do Informatid open another screen screenName do Text get tag TextBox1. then + get value PasswordTextBox1 * . Text then set VerticalArrangement1 (Visible i, to false set VerticalArrangement2 2. Visible to true set Label2 Text to Wrong username or password! Try again Viewer when Log_in Click do call FirebaseDB1 when Sign up Click do call FirebaseDB1- StoreValue tag valueToStore a Text GetValue TextBox1 Text TextBox1 Text PasswordTextBox1 tag valuelfTagNot There NA when FirebaseDB1 GotValue when Start Click tag value do Informatid open another screen screenName do Text get tag TextBox1. then + get value PasswordTextBox1 * . Text then set VerticalArrangement1 (Visible i, to false set VerticalArrangement2 2. Visible to true set Label2 Text to Wrong username or password! Try again