In GlassFrog you cannot add/edit the Circle Lead/Lead Link's accountabilities.
The reason behind this is that a circle’s Circle Lead/Lead Link inherits the purpose and any accountabilities from the circle itself, and controls any domains defined on the circle, just as if the circle were only a role and the Circle Lead/Lead Link filled that role.
In practice, the Lead Link's specific accountabilities can be deferred to another role, but GlassFrog doesn't have the capability to show that, so those will remain in the Lead Link's accountabilities list. (Circle Leads do not have specific accountabilities, as such, except for those on the circle itself.)
For reference, here is Article 2.2.3 of the Holacracy Constitution (version 4.1):