Hi Ravani,
As mentioned on the error message, if you need to AJAX refresh something, then the method needs to be Ajax Refresh, Submit is not at all the solution for this use case.
For more information on what the difference between Ajax Refresh, Submit and Navigate methods, you can see for instance this post.
Without the OML or more information, there's not really much that one can analyze to help you with. Can you perhaps provide more insights and screenshots about what are you trying to refresh and what does your action PopulaMedico looks like?
What are you refreshing or trying to refresh inside your PopulaMedico action? Is it an element of the list?