How to unlock: Talking to Arechi in the Vast Interior district (M16.5).
Arechi is one of the lascars and you can find him in the south-eastern part of the Vast Interior (M16.5). Talk to him, and you will discover that he and his allies are lost, and are looking for the entrance to the Anchorage.
For the needs of the described mission you must reach the Maw in the Small Nihilesh district (M19.5) and once there, open a portal leading to the Lost Anchorage. This action is a part of another side quest - The Newborn Maw. Move on to its description and complete all of the tasks mentioned there. This will result in you gaining the ability to teleport to the Anchorage.
There's also an alternative solution, which is available only if you have the Transdimensional Scalpel. The item is awarded for completing a quest called A Hilt Without a Blade, which is unlocked in The Vast Interior (M16.6). You can use the scalpel to make an incision and open the Maw. Mind you, however, that doing so will anger the Bloom and can have consequences in the future. The upside to this solution is that you don't have to worry about Gar-koto's quest at all and can go straight through the portal.
After you arrive at the Lost Anchorage talk to Captain Janur in the main hall (M21.1) and during your conversation tell her about the lost Lascars.
Now you can return to Arechi and tell him the news about the newly opened portal to the Anchorage. As a reward you will receive 25XP and the Changing Tool cypher (bonuses to the Quick Fingers and Smashing skills).