Hi Kyle,
Admins can send password resets via the "Users" tab. Please review this guide for step-by-step: https://help.whmcs.com/m/v80/l/1301340-where-is-the-reset-send-password-option
If a user no-longer has access to their email or is experiencing delivery problems, then staff would assist them in changing the email address to one which is functional, and send the password reset there instead.

In v8.0 and above we introduced a significant update to the authentication and authorization system for accounts and users in WHMCS. Client Accounts no longer have passwords, authentication is now done via Users.

v8.0 and above intentionally does not expose or permit direct manipulations of User passwords via the UI or in emails. Instead an email-based invitation and reset process is used in line with current best-design and security practices. This paradigm is common to many modern SaaS systems.