I can assure you Capsule Docs (where you posted this) has nothing to do with DHCP.
Based on your past questions, which have been about the 730 Appliance, I moved this to SMB and SMP.
Please post your queries in the appropriate space.
That, plus providing more details about your situation in your initial question, will increase the likelihood you will receive assistance from the community.
I assume you're asking how to create a static DHCP entry on the 730 Appliance.
You do this by creating a network object and specifying the MAC address of said device:
You can also do this from the Active Devices view by locating the relevant host, right-clicking, and do a Save As > Network Object.
If you're talking about the IP that the 730 receives from an ISP on its WAN interface, there is no way to control this from your end.