From my own terse notes:

Apply dissector for non-standard/different port # - e.g. for WebSocket (or BACnet/IP)

• Right click on grid column

  Right click "Source Port" field, click "Decode as", change "Current" DDL to the relevant protocol/dissector, "OK" for temporary or "Save" for permanent.

  To add one: Select "TCP Port" in "Field", set the port # in "Value", set the relevant protocol/dissector within the "Current" DDL.