How do I use pull down on this program?

A screen shot’s next to useless, since it only shows a part of the code.

Copy and Paste the code rather, inside </> tags.

But a pulldown resistor, if that’s what you mean, is an external resistor from an input pin to ground. (There are btw built-in pullup resistors, but no bulit-in pulldowns.)

Pictures of code? What am I supposed to do with a screenshot? Why don't you copy and paste the text so it is actually useful? Not only that, but the part you screen-shot doesn't have anything to do with any inputs. It's just a bunch of digitalWrite commands. So absolutely nothing to do with a pull-down there.

A pulldown resistor goes from the pin to ground. It doesn't go in the code. If you want to use a pullup then the chip has those built in and you can enable them from code.

Here's a good page for you to read. http://www.gammon.com.au/switches