Move forward twice and talk to the top-left troglodyte to learn the location of the shaman's cave. Move right twice and then enter the cave. Use the brushwood on the hearth. Light a match from the matchbox in the inventory and use it on the brushwood in the hearth. Talk to the shaman to receive the third part of the inscription. Time travel to the house. Space travel to the ruins:

Move forward and select the hole in the tree to take the fourth part of the inscription: