How Can I run Tomcat again

When I develop a web application.I delete .idea file.Then I reimport the project.I have .idea again.
But I can't run Tomcat 9;I lose my war file.I think I need a new war file.
So I build a new war.But the output layout is different from a web application.Although I can run Tomcat 9.But I can not get access to any resource.It gives me a 404 error.How can I fix this.Thanks!