To change default.Html page to default.cshtml page

Question

Hi,

 

  I faced a scenario like I add the new html page in MVC flow and set it as startup page and while running it appears first.

 

now again I need to set back the startup page as cshtml page ..but no option thre to go with

 

Can someone tell me how to change this .. I don't find any option in cshtml file as 'set as startup page'.