I have uploaded the sample QVF in the below link. To do what if analysis please download Variable extension and once it appears in your chart the rest is very easy. I have put an example for inoput box like and list box like using the same variable extension.. Very easy to use.
It's been a while since I've played around with the qsVariable extension....you might want to make sure you've created the variable in your application by going to the Variables editor. Create your variable there first, with an empty definition, then go to your qsVariable object in your sheet and name it the same as the variable you created. After that, you should be able to follow the step-by-step I created before and it should work.
I`m new to qlik sense, i`m looking for the same type of user input for my dashboard, i have tried adding input extension and followed the same steps as mentioned in these conversation, but still i`m not able to get the connection between input box value and my other graphs.