How to replace a broken tower bar
First, loosen the setscrews, these are the slotted screws on either side of the bracket. Use a small flat head screwdriver, the kind you would find in an eyeglass repair kit or a computer repair kit.
Next, carefully remove the bar from the wall.
Now, remove the broken rod and dispose of it.
Place a new rod into the brackets.
Put the new bar back onto the wall brackets.
Tighten the screws, while holding the bar in place until the screws can hold it.
To avoid loosing the small setscrews, do not loosen them all the way. Remove the unit with setscrews loosened, but still in place.