How do you do superposition to find value of voltage source
Instead of thinking 'replace each voltage source with a short', think 'turn down all voltage sources to 0 V', and do the same with any current sources. They will still be short or open respectively. It comes to the same thing, but I find it's sometimes easier on my brain if I don't have to remove components, only change their value. Where it can be handy to replace zero volt voltage sources by a wire is if it helps you identify resistors that can be combined in series or parallel.
The solution for all sources at zero is trivial, zero everywhere.
Now turn up each source individually, and solve for that one, with the others set to zero. Now add all the solutions together.