appname.herokuapp.com is redirecting me to www.appname.com after deployment

I got a project which is deployed before in evolix server with the domain name www.appname.com ( OVH domain ).

I migrate the project to heroku. After deployment when i click on the link appname.herokuapp.com it's redirected me to www.appname.com which is down as our project is no longer in evolix.

can someone explain me this issue ? and what should I do to fix it ?

I spent so much time looking for a solution but i didn't find something useful is this situation.