The maximum number of apps for free development profiles has been reached
The easiest way to solve this is delete these unfinished apps from your devices. Just delete them like you would any other app - directly on the phone. 

You can also use the "Devices &amp; Simulators" window in Xcode to delete them. If you have a lot, it is perhaps a bit faster.

If you have deleted the apps, but still get the error, then you need to remove the profiles themselves also. You can do that from the same "Devices &amp; Simulators" window by right-clicking on the name of your iOS device, selecting "View Provisioning Profiles" and then removing them.

You can also do that on the device in Settings > General > Profile. Choose each no longer used profile and then "Remove".