Mooshi-app seems to default third value on meter screen as “real power”, which is also a button which opens menu with “thermocouple k” as an option.

Keep in mind that k-type thermocouples need both channels, so you can only measure/log temperature.

Forums own search is pretty bad, you should use google site-search instead:
https://www.google.com/#q=site:https:%2F%2Fmoosh.im%2Ff%2F+thermocouple

Edit: Also it is voltage that k-type probes output, not resistance.
Actually that voltage depends on the temperature difference between ends of your probe (it does not matter what happens in the middle of that probe). Thats why you need two channels, as you have to log internal temperature of mooshimeter and then calculate what the temperature on the other end is from internal temp and k-type voltage. If you try to do it manually, you will hurt your head :D (if it in some point seems easy, you’re doing it wrong ;D)