Hello ,
Few questions before I can answer your question.
1> Is the product used ACS or Campaign V6/V7
2>. Sub-domain delegation to Adobe is a complete process which needs to be completed by Adobe if it is Hosted by Adobe Managed Services. The details of the step are given here : https://docs.campaign.adobe.com/doc/AC6.1/en/Technotes/AdobeCampaign_Deliverability_Sub_Domain_Deleg...
In short , if you have got the sub-domain configured you need to point the name server records to Adobe and then open a support ticket so that Adobe can set the branding to be used with Campaign.
Regards,
Adhiyan