How to bring back Wishlist option for an app which is showing as installed in playstore but not actually installed on my device? I recently came across some apps in playstore and I want to install those apps. Since I don't have sufficient internal memory I can't install them. It says 


  Error downloading app "xyz app". There is insufficient space on the
  device.


So I want to save those apps to my wishlist and install it later until I free up my phone's internal memory. But once I got the error message that I mentioned above the Wishlist icon in the Playstore app and Add to wishlist button in http://play.google.com are not visible for the apps that I tried to install.

Weird this is when I haven't installed the app, the web version of playstore is showing "Installed" and my mobile PlayStore app is Showing "Install" button. And the app is not listed in "My Apps" section. 

Hint: I guess the problem will be solved once I turn the "Installed" button to "Install" button in the playstore website which in turn will bring back the "Add to wishlist" button. But how can I do that?
When you mentioned the "app is not listed in 'My Apps' section", do you mean the 'Installed', 'My Apps' section or the 'All' 'My Apps' section? 

I think they should be listed in the 'All' section, and therefore, you won't be able to add them to your wishlist because you already have them, even if they aren't installed. 

If you go to the 'All' section in your Moto G and find the apps, if they are there, and then press the 'cross' icon for each one, the apps should be removed from your 'My Apps' and you will be able to add them to your wishlist. This will only work if the apps are free because trying to remove paid apps from 'My Apps' means they don't display in 'My Apps' but are essentially still there because you have paid for the apps and Google doesn't want you to discard them. 

If the apps are paid, you can refund them (either using the 'Refund' button which will display near the apps for a limited time after purchase or, I assume, contacting Google). The apps will then be removed from the 'My Apps' section and you will be able to add them to your wishlist. 

If the apps don't display in the 'All' or 'My Apps' section, try clearing the data and cache of the Play Store and then signing back in your phone and see if the situation changes and if it doesn't, I would ring Google support because they have the power to sort out stuff on the server-side.