In GlassFrog, Cross-links are treated as normal "Defined Roles". This means you would have to create a Cross-link during governance meetings in both circles.
Another way to think about this is that cross-links can also come from outside of your organization, in which case you wouldn't need two meetings (but presumably the other organization would have some process to put a person in that role.)
See Holacracy Constitution Article 2.7 for information on Cross-Links.
Cross-links can also be created by Policy, in which case the Secretary can create the Role by opening a Governance meeting by themselves and making the change.