Hi, welcome!
Aruba 5400R zl2 MM (Management Module) hasn't any "interface" ports (excluding OoBM and Serial Console ports) that you can use to uplink for normal (non-OoBM) access traffic.
To uplink (or to downlink) - well, simply...to link - to other Switches or Access devices you need to populate with proper interface modules one of its 6 (or 12) alphabetic identified free slots.
Look at Aruba 5400R zl2 Datasheet to find a suitable module (I suggest you to use only latest v3 zl2 generation modules).
Old but still good HP 5400R zl2 FAQs.
Aruba 5400R zl2 Option Parts.
Aruba 5400R zl2 v2 zl to v3 zl2 Modules Compatibility and Upgrade Guide .