Lately, I've been doing a few Office 365 migrations. I've run into a snag with a couple of service accounts and making sure their passwords do not expire.
Within the Office 365 portal, you can make global changes but you cannot specify one account. To set one account's password to not expire you'll need to use PowerShell.
Below are the commands you need to run-
Connect-AzureAD Set-AzureADUser -ObjectId <user id> -PasswordPolicies DisablePasswordExpiration