How to remove accessory from player character?

Don't use 'for i =' loop if you want to remove hats.

Use this method instead:

for _, v in pairs(char:GetChildren()) do 
    if v:IsA('Accessory') then 
        local accessory = v
        accessory:Destroy()
    end
end

The reason might be that your script is running before the character's appearance has loaded. To do that you add repeat wait() until Player.HasAppearanceLoaded

Player.HasAppearanceLoaded returns true or false.

game.Players.PlayerAdded:Connect(function(Player)
    Player.CharacterAdded:Connect(function(Character)
        repeat wait() until Player.HasAppearanceLoaded

        local Find = Character:GetChildren()

        for i = 1,#Find do
            if Find[i].ClassName == "Accessory" then
                print(Find[i])
                Find[i]:Destroy()
            end
        end
    end)
end)

You can use the Humanoid:RemoveAccessories() function.

plr.CharacterAdded:Connect(function(char)
    char:WaitForChild"Humanoid":RemoveAccessories()
end)

Or you can use an event called ChildAdded and check if the child is an Accessory

plr.CharacterAdded:Connect(function(char)
    char.ChildAdded:Connect(function(c)
        if c.ClassName == "Accessory" then
            game:GetService"Debris":AddItem(c, 0.1)
        end
    end)
end)