Sign into Office 365 admin center and view the Security and Compliance center.
Look for the “Content search” and put in the sender/subject etc.
Once the search has completed, open a Powershell Window
$UserCredential = Get-Credential
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://ps.compliance.protection.outlook.com/powershell-liveid/ -Credential $UserCredential -Authentication Basic -AllowRedirection
Import-PSSession $Session -DisableNameChecking -allowclobber
New-ComplianceSearchAction -SearchName “contentsearchname” -Purge -PurgeType SoftDelete
or
New-ComplianceSearchAction -SearchName “contentsearchname” -Purge -PurgeType HardDelete
Get-ComplianceSearchAction -Purge
