I want to give you meaningful advice but I don't know where on earth you reside, deserts of the Middle East, South Pacific, North Dakota or Florida. It makes a difference. Fill out your profile as to "location" please, please.
Generally, you will be able to solve the biggest part of your problem with a lonely lone chick by placing it in proximity to other chickens. Many people find themselves with one baby chick, period, and that's much harder to deal with.
It can be as simple as letting it visit with the older chickens from the safety of a cage. In fact, I would first integrate the new one with the older chicks by means of a partition in a pen. Let them get acquainted, then in a few weeks, put them together.
Day trips out to visit with the older flock is a great way to begin integration. Pick nice days and bring them back as it gets cool. Even at a couple weeks old, chicks are able to spend time away from heat and it helps acclimate them to cooler temps.
The time to get started is now.
