There are times I have needed to adjust the safe senders list of a user on Office 365/Microsoft 365. If you are the administrator of the tenant, simply fire up Powershell, then:

$Credentials = Get-Credential
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri -Credential $Credentials -Authentication Basic -AllowRedirection
Import-PSSession $Session -DisableNameChecking

Get-Mailbox -ResultSize Unlimited | Set-MailboxJunkEmailConfiguration -TrustedSendersAndDomains ""

First 3 lines gets you connected to Office 365, when prompted enter admin email/password

Then last item gets list of mailboxes and adds to safe senders list. If you need to just change it for 1 user, you can do something like:

Get-Mailbox -Identity | Set-MailboxJunkEmailConfiguration -TrustedSendersAndDomains ""

This will do the trick