Alright, now that the scene is up and ready, you need to set the target platform of your choice. In the Menu Tabs, Click on File -> Build Settings...
Here, select your target Platform on the left side "Android" or "iOS" and Press
"Switch Platform" ( You should have Switch Platform instead of Build in my case).
Then, Delete the old scene if any and Click on "Add Open Scenes"
Once it's done, you can close this window and go on to the next step :D.