Self service password reset for external user Office 365

If you have an administrator privilege you can set it on Azure Administration center: Let people reset their own passwords These steps turn on self-service password reset for everyone in your business. In the admin center, go to the settings > Org settings page. At the top of the Org settings page, select the Security & Privacy tab. Select Self-service Password Reset. Under Self-service password reset, select Go to the Azure portal to turn on self-service password reset. On the Properties page, select All to enable it for everyone in your business, and then select Save. When your users sign in, they will be prompted to enter additional contact information that will help them reset their password in the future.