Well, this is different from homepage. for setup this page you need to provide page content. you can provide this content from your dashboard. just follow those steps and you will be able to provide content.
go to Admin Dashboard > Pages > About Us , here you will find a text box with the title of content, in this box you can provide your about page content.
make sure the right sidebar visibility option is visible and the bottom template box template suffix is page.about selected. Then save it and go to customize theme again. you can see two tabs on the left sidebar called section and theme settings. go to theme settings tab and find the about page tab, click on it. then you can select an image for about page.