This achievement occurs during Episode 1 - It's About Time
Once inside Doc's place:
• Walk into the back room with Biff.
• Interact with Town Square Model.
• Dialog (Biff): Any
• Interact with Amplifier Controls
• Interact with Marty's Guitar
•
Use Item to equip Marty's Guitar
• Interact with Amplifier Controls (With Guitar equipped)
• Interact with George.
• Dialog (George): "I can fight my own fights, Dad."
•
to exit conversation.
• Interact with Marty's Guitar.
Achievement pops once you're in the back alley
Credit to T_l_M_B_0 of PST