This can be done in Instant Action Missions and Co-Op. Help me give credit to those who discover something new. I feel like this could be the thread where all the steps won’t be buried into the comments cause I want everybody to find this skin as a community :)
Shoot Hondo painting in Maz’s castle
Go to Slave I
By the U-shaped tree right across from Slave I, interact with the small objects by going first, last, middle (THERE CAN POTENTIALLY BE 3 COINS TO FIND TO PLACE THEM IN THOSE CYLINDERS, credits to u/lukecat44)