This addresses the general question rather than your specific question.
You can fill in the environmental details that are specific to your own world.
Imagine yourself living in such a situation for many years, and ask yourself this question:
- What do I find most significant about my body, that if changed slightly, would make my life better?
For evolution, "better" means making it more likely that you and/or your offspring will have a better than average survival rate, whether by directly helping you to survive dangerous situations or by indirectly helping you to be more prosperous and able to support a larger family.
If for instance, you think that having longer arms would help, then among the general population you know that those with longer arms will live slightly longer and have more children that will survive to have children of their own. Similarly, those with shorter arms will tend not to prosper as well, resulting in dying sooner, or having fewer surviving children.
Even if the effect is small, as long as it is significant, after many generations, the general population will have longer arms than does the current population. There is of course a natural limit to arm length, and eventually your people will end up near that limit.
Apply that same principle to several different physical attributes that will make life better in your specific environment, and project those changes into the future, and that is what your new "race" will eventually look like.
Despite the popular view, evolutionary adaptation isn't a case of everyone suddenly developing new features to help them survive a new environment. It's a case of killing off those that don't already have the appropriate features.
A specific example is the blatant difference between human groups that lived for thousands of years in regions close to the equator or far from it. Those close to the equator will have received much more direct exposure to sunlight, both because of the intensity of the light and because of the clothing worn. Near the equator, those with lighter skin will be more likely to get sunburn and skin cancer, while far away, those with darker skin will be more likely to get rickets. The two different environments favour two opposite effects of melanin, and those that don't have the appropriate genes will produce fewer surviving offspring.