If you want to install ios apps from a third-party vendor without jailbreaking your device, only one software helps you to do the same. Cydia Impactor is software which helps you to sideload any apps on your ios device without jailbreaking device within 1min. Download it from cydiaimpactor.online
Now connect your device to the computer with a cable and upload app file which you want to install on your device. It will transmit your apps to your ios device and you can then install it.