Tutorial by words:
To do this high damage game mechanic, you'd want to switch between the Dragon Slayers and the Azure Periastron extremely fast.
What I did was I had my ring finger on the Dragon Slayers (Key 1) and my index finger on the Azure Periastron (Key 4). Then, I proceeded to press them both AT THE SAME TIME as fast as I could. This gave the illusion of an autoclicker. However, I'm sure that's not how autoclickers work.
Use your mouse to angle your blades into Whigmaster. If he tries to climb on your avatar, try to have your character facing -22.5° (you're facing Whigmaster a little more). If you're lacking damage output, turn your avatar -45° (completely diagonal); this assures that Whigmaster receives the most damage in contact with your blades.
Roblox melee gears can produce extremely high damage depending on how much movement is between (for example) a sword and the player. Think of it like barbed wire; the more you move, the more you're injured.