After reaching friendship level 6 with Buzz, talk to him to start The Fragmented Past quest. You also need to have Remy and Scar unlocked. Follow these steps to complete the quest:
Go to the river in the Forest of Valor with Buzz
Search for a buried clue about Buzz’s past along the river in the Forest of Valor then talk to Buzz
Talk to Scar
Gather the following meals and bring them to Scar
Search Scar’s Cave for an object proving his past friendship with Buzz
Fish the next clue from the river on the Sunlit Plateau
Open your Inventory and investigate the Old Fishing Rod then talk to Buzz
Listen as Buzz talks to Scar
Return to Buzz
Step 1: Go to the river in the Forest of Valor with Buzz
After talking to Buzz, he mentions that the remembers something about being in the Forest of Valor.
Step 2: Search for a buried clue about Buzz’s past along the river in the Forest of Valor then talk to Buzz
Go to the bank of the river in the Forest of Valor and look for a dig spot. Use your shovel to dig the item out and then inspect it to find a piece of a memory. Report back to Buzz and he will want you to go talk to Scar to find out why he was in the memory.
Step 3: Talk to Scar
Go talk to Scar to ask him why he was having a fight with Buzz back then. Scar will then ask you to prepare him some meals first before he talks. He will then give you some recipe books for the dishes he wants.
Step 4: Gather the following meals and bring them to Scar
Open up your inventory and use the recipe books to learn the ingredients of the dishes. You will then need to cook the following meals:
After cooking them, go back to Scar and hand the dishes over. Scar will then reveal that he was friends with Buzz before the Forgetting happened and he wants you to go search his cave for a clue.
Step 5: Search Scar’s Cave for an object proving his past friendship with Buzz
Go inside Scar’s cave and you’ll see the Space Ranger patch on the ground. Inspect it and then talk to Buzz about the new piece of memory that you’ll see.
Step 6: Fish the next clue from the river on the Sunlit Plateau
Head over to Sunlit Plateau and look for a gold ripple in the water. Use your fishing rod to fish out the item which turns out to be an Old Fishing Rod.
Step 7: Open your Inventory and investigate the Old Fishing Rod then talk to Buzz
Inspect the Old Fishing Rod in your inventory to see the final piece of the memory that shows what actually happened back then with Scar.
Step 8: Listen as Buzz talks to Scar
Follow Buzz and listen to his conversation with Scar as they clarify what they were doing in the past.
Step 9: Return to Buzz
After the conversation, talk to Buzz once again to complete the quest.
After completing the quest, you can then continue working on leveling up your friendship level with Buzz.