Not sure what you are asking here, broke as in not working? or broke as in pieces of glass are in the tank? If the heater is not working, you need to purchase a new heater. If the glass tube is cracked or broken and pieces of glass are in your tank, then you need to unplug the heater and remove the glass from the tank.
Add an aquarium heater. Make sure you choose a heater with the correct wattage for your aquarium's water volume.
what type of aquarium tropical (heater needed) cold water or marine (saltwater)
Bc its broke
A fish aquarium will be fine or a tank with a lid shall do
What you have to do, is replace the heater core itself
A 50 watt heater is major over kill for a 3 gallon tank, a 10 watt heater is more than enough for a tank that size. You will nuke your aquarium very quickly the first time the 50 watt heater sticks on, with a 10 watt heater if it sticks on the aquarium temp will only raise a degree or two.
because it broke.
Take - him - to - a.... VET ! Get him seen by a professional !
because it's broke
On most any heater, yes. The temperature you'd commonly be looking for is about 76*-80*F. This will vary though depending on what you're wanting to keep.
Usually when you purchase a water heater for the aquarium, It keeps the temp between 72-78 degrees. I have a ten gallon tank with a heater in it and have never had a problem.
There are many necessities when setting up an aquarium. One will need a tank and proper lighting. A skimmer to skim the water, rocks, a heater, and regular maintenance tools are required as well.