forgot my pass word on my airport express,how to make new pass word

You can try to find the password in your keychain. Start Keychain Access.app under Application/Utilities.

If you cannot find it you have to reset the Airport.

Try this User Tip from forum expert Tesserax:

AirPort - Regain Access from Forgotten Passwords

If no luck here, then study the information about a Soft Reset in this Apple support document to reset your password(s):

Resetting an AirPort Base Station or Time Capsule FAQ