Adding elevation data to observations has been discussed in the past, and it’s unlikely we’ll be implementing it. https://forum.inaturalist.org/t/altitude-on-observations/1476
I would probably download a CSV of data (eg Pinaceae in California) and use a separate program to see which ones are above a certain elevation, going by coordinates and topographical maps. Even then, you’d have to take into account the accuracy of each location, which could throw things off quite a bit.