i have forgotten my user account password, what should i do ?

Assuming you are talking about the 2015 MacBook Air, restart and hold the Command and R keys. When it has restarted, from the Utilities drop down menu choose Terminal, and when Terminal opens type EXACTLY:

resetpassword

and press Enter. When the Reset Password window opens, select the internal drive, and then the user, and then type a new password twice. Then Save and accept the next dialog window that opens. Lower right of the Reset Password window apply the reset of user home directory permissions. Go to the apple left side of the menu bar, Restart.

Yes, will work on any account.

You are very welcome, it was a pleasure to be of assistance.