Can living at a higher altitude for example el.paso texas cause.mild.right heart enlargement? is that even possible?

NO: Only if you also have superimposed lung disease.

Maybe: High altitude has lower oxygen content so living at high altitude causes adaptive changes to compensate for this. heart size and function are some of these changes. this is why some people train in high altitude prior to competition. a heart condition can be exacerbated or improved by changes in altitude.