But EASIER method:
1. Browse into "[drive]:\ProgramData\BlueStacks\UserData\InputMapper\"
2. Find "com.supercell.clashofclans.cfg"
3. Open it with notepad
4. Clear the contents and paste this:
[Keys]

Down = Swipe Up (20,50); Swipe Down (60,20)
Up = Swipe Down (20,50); Swipe Up (60,20)

[Guidance]

Down = SDown
Up = SUp


[Gamepad]

A = Down
B = Up


[OpenSensor]

Mode = Tap
A = Up SUp
B = Down SDown

[Strings]
SDown = Zoom Out
SUp = Zoom In
5. Save the file and quit bluestacks from task bar side panel and start again.
6. DONE!!!
[Note]
If you couldn't find "com.supercell.clashofclans.cfg" (as was my case), create or duplicate any other cfg file n rename n follow from step 3


HAPPY BOTTING 'N' CLASHING