It's sort of a PITA. Click on the name of the person who sent you the LUT in iMessage and scroll down to "Documents". Tap on the LUT file. Use the Share button

It's sort of a PITA. Click on the name of the person who sent you the LUT in iMessage and scroll down to "Documents". Tap on the LUT file. Use the Share button in the lower left corner and then, where it lists the apps, tap "More". You'll see Kino listed. If you tap it, it will automatically import it. Again, PITA, but given the iOS infrastructure, I'm surprised it works at all.