Need to add Feature to C# Code for Unity 2D Game.

Hi There , I need some one to Modify/Add some feature to this code . This code is an Unity drag and drop game as shown in this Youtube Video: " [login to view URL]" this code works perfectly fine. but The requirement here is , once the object is place in its correct position, its still moving. i want to lock the object (can't drag once places in its correct spot). for the LOCK feature here is a reference from another video: "[login to view URL]"