You need a lightning to USB camera adapter. This one:

You can get it on the official website of Apple. Or you can search for analogues on AIiexpress, they will be cheaper, but no guarantees that they will work, so it’s a risk. In order to connect the controller, you need to connect it through this adapter to your phone or tablet, go to the Settings section, then go to the MIDI section. The controller should appear in the Menu, as soon as it appeared, you need to click the connection button. After this, you need to adjust the pads' correspondence to the real buttons, by clicking the pad in the MIDI section and then clicking the pad which should match it on the controller. So it is necessary to do with all 12 pads. After that, the controller will be ready for operation. You can go to the main screen and play.

Please watch this step by step tutorial: