I cannot locate the command "Export for DPS" in ID 2015. There is no such option under Export in Indesign menu. How can I do that?
You have to sign up for the beta as mentioned. From there you can download the export filters as well as a working Overlays panel.
Since a similar question was posted in the other DPS forum, I suspect there's some confusion here. If you are trying to just keep using what you used with CC 2014, the following may be useful:
"The new release of InDesign CC 2015 has arrived to Creative Cloud members! This new InDesign version supports creating content for the new Digital Publishing Solution (DPS 2015). To create articles for DPS 2015, use any version of InDesign from CS6 and later. DPS 2015 is available in Beta. For more information, see http://adobe.ly/1dHUvku.
To create content for Digital Publishing Suite (DPS) you should use InDesign CC 2014, InDesign CC, or InDesign CS6.
Installation changes: Unlike previous installations of CC, installing CC 2015 will uninstall previous versions of InDesign on your computer. To retain the previous version, make sure that you click Advanced Options and deselect "Uninstall Previous Versions." For more information, seehttp://adobe.ly/1C9L831.
If previous versions of InDesign were uninstalled on your computer and you would like to install them again please, see this help topic for step-by-step instructions: http://adobe.ly/1enSriu"