Source: Resetting a user’s password through the CLI – Moodle Tips

If you have access to the Moodle server, you can use the admin/cli/reset_password.phpscript to reset passwords for users with the manual authentication method.

To run this script (from the moodle root code directory), note you may need to sudo as a user with write privileges to the $CFG->dataroot directory.

php admin/cli/reset_password.php

== Password reset ==
Enter username (manual authentication only)
: moodletips
Enter new password
: moodletips

Note the password you specified has to match the password rules configured in Moodle for example the above password moodletips by default would throw:

Passwords must have at least 1 digit(s).
Passwords must have at least 1 upper case letter(s).
Passwords must have at least 1 non-alphanumeric character(s) such as as *, -, or #.

Very handy if you are unable to get into the Moodle site for any reason, or need a quick way to reset a user’s password.