Open Azure Data Studio and execute these commands:
-- create login credentials on the server
USE master;
CREATE LOGIN user_name WITH password='p455w0rd';
GO
-- create user on the database
USE DATABASE_NAME;
CREATE USER user_name FROM LOGIN user_name;
GO
-- grant permission for user
USE DATABASE_NAME;
EXEC sp_addrolemember 'db_datareader', 'user_name';
EXEC sp_addrolemember 'db_datawriter', 'user_name';
EXEC sp_addrolemember 'db_backupoperator', 'user_name';
GO