With the F5 BIG-IQ tool you can update the admin and root passwords for all your devices you manage or just a select few and its fast and very easy to do.

When you manage BIG-IP device from BIG-IQ Centralized Management, it is good practice to change the default admin and root passwords on a regular basis. From BIG-IQ, you can change the passwords for several BIG-IP devices at one time.

Note: You can change the passwords for several BIG-IP devices simultaneously only if they have the same password.     Important: The passwords for the BIG-IP devices you select must all be identical.

1. On the top of the BIG-IQ GUI, click Devices tab.
2. On the left, click PASSWORD MANAGEMENT > Change Device Passwords .
3. Near the top of the screen, click the Create button.
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4. In the Name and Descriptions fields, type a name and optional description to help you identify this task.
5. From the Available list, select devices and move them to the Selected list.
6. Select an option for the Change Password setting.
7. Provide the old and new passwords, as required.
8. Click the Run button at the bottom of the screen.
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    BIG-IQ will apply the new password to all of the selected BIG-IP devices. You can view the status of this task from the Change Device Passwords screen.

REFERENCE: https://support.f5.com/csp/article/K25546160