There are no direct flights from Kathmandu to Simikot
The possible way is by considering a connecting flight to Nepalgunj/surkhet, which means you have to take the flight from Kathmandu to Nepalgunj/Surkhet and then from Nepalgunj/Surkhet to Simikot.
There is still another option, which may not be practical for all. You can charter a plane. This option can be considered if you have enough group members in your team.
Instruction on How to Book Flight from Kathmandu to simikot
In this process you will book 2 different ticket/sector independently.
Other Important Links
All rights reserved. Nepflights.com