I'm surprised that no one responded to your question. I am also a Sig newbie, but no stranger 1911-type take down which is what the P290 is. I have to tell you, I don't think I'm going to be able to field strip this pistol by myself without rigging a stationary punch to push the slide release out from the other side while I hold the slide back in the proper position with both hands. In every other 1911-type field strip that I have performed, I was able to hold the slide back with one hand with my thumb one the back strap and four fingers wrapped around the slide. Then I could manipulate the removal of the slide stop with the other hand. I can't do that on the P290 because of the small size and recoil spring tension. It takes both hands.
And then how in the devil am I going to get the slide release back in without a third hand. I too would like to hear what others are doing to field strip this pistol.