The influencer's profile is automatically added to your directory when their profile is added to your campaigns.
This process applies when any influencer has published a post in one of the campaigns.
You can also manually add an influencer to your directory to use for a future campaign:
Go to the influencer's profile in Lefty.
At the bottom of the side tab on the left, with all of their information, you will see a button labeled "add to directory," where Lefty will upload them.