This article outlines the process for adding and removing mobility print printers to iOS devices. Sometimes as printers change, it becomes necessary to remove printers you have set up previously, and re-add them to pick up those changes on your device.
A quick distinction - mobility print is not an app. It exists as a configuration profile under your settings app. So the process for installing it may be a new and different experience.
Installing Mobility Print
Uninstalling Mobility Print
Printing on iOS