ManagerDN from Okta to Azure AD

I’ll first set the stage and then ask the question. MS does not allow you to assign manager to a user that is in a different forest. To get around this, we’ve created matching contacts in other domains for managers so they may be assigned to users. When the manager field gets imported into Okta, the DN of the contact shows. I am provisioning O365 accounts through Okta, thus creating Azure AD accounts. Because the DN is used for the manager all the way through, this contact entry does not match another user when it gets to Azure AD. Here is my question.

I’ve been able to grab the first and last name from the mangerDN field of the user which in this case is the contact I’ve created. This the expression that I used:
(substringBefore( substringAfter(appuser.managerDn, “=”), “,”))

Now I would like to take this first and last name, match it to the “real” manager account in Okta and populate a field that user’s DN.

Anyone have any insight into how to do the user match?