Depends on if you still want to own an FC, want to sell, or want to sell to an FC that will allow you to be a member/merging with another FC.

If still own, obviously just advertise your FC. Pay people gil to join and offer to help them out a lot by doing things like crafting gear for them to incentivize.

If want to sell, someone already mentioned how valuable a fully leveled up FC house can be to someone who doesn't want to be in an actual FC but still have the benefits of owning one for personal use.

If merging, advertise in party finder.