How to set specific Meta Tag values while creating Article Content.?
You don't need any code for that, that Metatag module has that functionality built into it

These 2 listed features could apply to your use case specifically:


  
  Per entity and per entity bundle to control default meta tags for all items of a certain type, e.g. all nodes of a certain content type.
  Ability to override meta tags on each entity object, e.g. to override meta tags on an individual node.