Go to www.spinbackup.com and create your Spinbackup account. For signing up, check our How to sign up for Spinbackup account for Business article.
Automatic backup of your Google Sites will start the day after you sign up.
If you want to start the backup of your Google Sites manually, follow these steps:
Tap the Log in as G Suite Administrator button in the upper right corner.
Insert your e-mail and password or sign in with Google.
On your dashboard on the left, click Users.
You will see a list of all your domain users subscribed to Spinbackup. Choose the name of a user whose Google Sites must be backed up, unfold it by clicking +/- button, and click the Google Sites button under the user name.
In a new window, press Backup.
When the backup process is complete, you can see all your Google Sites backed up to your Spinbackup account.
To learn more about how to back up your Google Sites, watch this video