TPMS information is shown in the manual, but nothing is available on powerparts. The part for the 790 Duke (P/n 64112932044. £114) is not compatible, the KTM tool cannot install it.
According to a dealer who asked KTM Austria the TPMS is still in development, and will be available later.
The install will be fairly involved: tires need to be removed to install replacement valves, a receiver plugged in, and a software activation done.
A cheap alternative, if you have a Zumo GPS, Garmin offers TPMS valves caps that connects to it.