Designer has been debundled from Acrobat since Acrobat XI and was replaced with the already discontinued FormsCentral.
Designer ES4 now available as Stand-alone version.
Acrobat DC now comes without Designer and FormsCentral.
If your Designer was bundeld to a previous Acrobat (8, 9 or X Pro) version it has been removed during installation of DC I'm afraid.
There is currentlty no know way to installa Acrobat DC parallel to existing Acrobat versions, so you'll have to decide which one you want to use.
I personally would not use Designer together with Acrobat DC, as the new UI makes it difficult to use the PDF-Preview etc.