How to select which file is previewed in codesandbox

I have a imported project in which I have files with following structure:

dir1
    index1.html
dir2
    index2.html

prewiew is showing me index1.html How would I change it to show index2.html in prewiew? I tried to change package.json file main attribute to "/dir2/index2.html" but it does not work

Solution

Codesandbox does not open the "main" file on opening a sandbox - it executes the "build" and "start" scripts in package.json (and other related scripts, such as pre-builds, etc), since that's what it needs to do to prep a package for running in their preview browser and/or node instance.