There are multiple steps which needs to be done to configure eDiscovery successfully in SharePoint Online or Office 365. To perform this you need to be Office 365 Tenant Admin.
Here is a checklist to confirm the set up for eDiscovery
- Have you created a Site Collection with template as eDiscovery Center?
- Have you configured Exchange Online as one of the Result Sources in eDiscovery Center?
- Have you created a Security group called eDiscovery Managers in Exchange Admin?
- Have you given access to security group eDiscovery Managers to Site Collection as Admin?
- Have you given Admin access to all Site Collections to security group eDiscovery Managers?
- Have you given read permissions to eDiscovery Managers to Crawl Log permissions in Search settings in SharePoint admin?
- Have you given access to Role Discovery Management in Exchange Admin to eDiscovery Managers?
If your answer to all above questions yes then you are ready and your eDiscovery Managers can create cases now.