Progress through the main story until you reach the area where Medalum is available
Defeat the enemy or boss that drops Medalum in Expedition 33
Open any chest or reward container tied to Medalum’s location
Complete the related side quest or optional objective if Medalum is a quest reward
Check the in-game shop or vendor if Medalum is sold there
Verify the exact unlock condition in your current chapter or region, since availability can vary by progression