The default username is “sa” and password “mobile123” or “admin123” is used in the demo
It is the password you provided at the time of SQL Server installation, if you used some other password then you should add that password here.
Remember what password you have given here at the time of SQL Server installation.
No worries if you don’t remember the password, now you can reset easily as follow
Step 1. Open Run command 
Step 2. Type “SMS” in Run command
Step 3. Select SQL Management Studio
Step 4. Connect SQL Server
Step 5. Expand Security -> Logins -> sa
reset password, select database, and save it.
