How do I assign an IPv6 address to a system?

I am working on assigning an static IPv6 address to a firewall.

If it was an IPv4 address, I can easily assign a static IP address like this:

If 10.10.10.13 is available in the 10.10.10.0/24 subnet then I can assign 10.10.10.13 to the system.

How would I select an IPv6 static IP address from an IPv6 subnet and assign it to the system?

Thank you.