Call 911, it's best to get help on the way just in case your not able to become the hero of the day. Do not rush to the edge of the hole to attempt to rescue. This may turn into 2 victims in the water instead. When trying to save somebody else that fell into the water remember the steps Preach, Reach, Throw, Row and Go.
Preach: Try to coach the person out of the water. Shout out words of encouragement to help them stay calm, fight and survive. Remind them to stay afloat, to never give up, that help is on the way.
Reach: If you're not able to talk them out of the situation safely extend and object like rope, paracord or even jumper cables. Try to stay on the solid safe ground as much as possible, do not go any further out on the ice than what's needed. If the victim begins to pull you in then release your grip and try again.
Throw: throw a line or something that can float. Try to have them wrap the line around their body before they become too weak to grasp it with their hands.
Row: Grab a small boat or floatation device. Row or float out to the victim or toss the floatation device out to the victim. If you're able to grab a boat then pull the person over into the boat.
Go: If all else fail you're just going to have to go get them, but it's best to let the professionals do this. If you must approach a hole don't walk upright, instead lay down and roll or slide to the edge. Spreading your body over a larger surface area will make the ice less susceptive to break more. But if it's too dangerous to perform a rescue then just call 911 and continue to verbally coach the person.