How can I reset a forgotten passphrase?

How to reset forgotten passphrase for user ?
How can I send invitation for user to reset passphrase?

You can’t. See. https://help.passbolt.com/faq/start/passphrase-recovery

Unfortunately it is not possible to reset your private key passphrase if you do not remember the original. Similarly if you have lost your private key and you do not have a backup, you cannot decrypt your passwords anymore.

Sadly, you have lost access to the passwords that you have not yet shared. If you have shared your password with somebody you can create a new account and ask them to share your password back with you.

If you can’t remember your passphrase, the best thing to do is to start anew.