In order to identify which type of information is consuming the environment storage space, you need to user the organization insights by installing it or accessing directly from the Power Platform Admin Center
First Option: Installing Organization Insights (Only available on version 9 or higher)
To get started, log into your Dynamics 365 instance. You will need to download Organization Insights from the Dynamics Marketplace found in Settings > Dynamics Marketplace.
Type “Organization Insights” in the search feature and click Get it now.
Agree to the terms and conditions and choose Continue.
Select the Dynamics 365 organization you want to add the application to it.
Agree to the terms by placing a check box in each item.
To confirm the solution installed, go to Settings > Solutions. You should see Organization Insights as a solution installed in your Dynamics 365 instance.
To view the new Organization Insights, go to Settings > Organization Insights.
Second Option: Accessing using Power Platform Admin Center
Open a internet browser and go to: https://admin.powerplatform.microsoft.com/
Once there, log in using the user credentials that has admin right
Now, go to Analytics > Common Data Service for Apps analytics > Storage
Under this tab, you should be able how the data is consuming the storage space.
Based on that information, you can set a bulk deletion to delete the data that is consuming the environment space
Scheduling a Bulk Deletion
Go to Settings > Data Management
Choose the option - Bulk Record Deletion
On the windows that shows all the bulk deletions, hit NEW
On the Bulk Deletion Windows, follow the wizard to define the criteria to the records that will be deleted based on the information that was get using the organization insight tool.
In some extreme cases, build a Kingsway SSIS delete job to clear the tables identified on the organization insight tool.