Vertical blinds are a type of window treatment that conceals the view through your windows. Unlike curtains, blinds open and close in slots with a twist rod, and also open all the way with the help of a drawstring. If the drawstring should break and become loose enough to fall out and get lost, you'll need to replace the string to continue opening the blinds completely. Most blinds are designed with a housing unit that can be managed by yourself, without the help of a professional.
Remove the blinds from the mounting bracket over the window. Depending on your brand of blind, the brackets may have a slat that you can slide over to allow the blind top to pop through the brackets.
Untie the knots that hold the plastic stoppers at the end of each string. Remove the stoppers and set them aside for future use.
Thread the new cord onto the long needle. Insert the new cord--following the old line through the upper casing of the blinds--until the needle pokes out where the old cord exits the housing. Use the screwdriver to press back the locking mechanism, which secures the cord at any given position in height, so the needle may pass through.
Pull through the old cord and discard it. Pull the remaining new cord through the upper casing until both ends are even. Remove screwdriver, allowing locking mechanism to pop back into place. Tie on the plastic stoppers.
Replace the blinds into the mounting brackets and slip the sliding covers back over the ends to secure the entire unit. Adjust the string length by using the screwdriver to release the locking mechanism once more. Cut off any excess string when the blinds are down, so you don't remove too much string.