GWS Enterprise Standard and Enterprise Plus users can ask for an additional 5TB storage for free.
To be eligible for additional storage, accounts must have been active for a minimum of 90 days and need to have at least 5 active users.
Google Workspace Enterprise Standard and Enterprise Plus customers who want additional storage can request more storage once every 90 days. Quota Increases are granted upon reasonable request at Google's discretion.
You need to request this additional space by raising a ticket with Google Support via https://support.cloud.google.com/portal
(Issue Type: GWS/ Category: Billing)
NOTE: There is a little catch regarding the minimum of 90 days activity. In case customer was moved to another console (https://channelservices.cloud.google.com/customers?authuser=0), 90 days is counted from the moment they are moved ( they can be with Google for years but sadly they will have to wait). In these cases I recommend trying to reason with Google a bit just to show how unreasonable this is, but still be very nice and polite and possibly they might give even more storage than customer wanted (I do not guarantee you will get more but this worked for me, so customer was super happy in the end and forgot about the whole waiting thing since he got more than he asked for).
Example of customer request for storage increase: https://ask.revolgy.com/a/tickets/123666