I accidently deleted the playstore app on my new Samsung mega phone How do I get it back ?

It shouldn't be possible to delete it, as QueenNewt implied, though you can disable it. This issue arises a lot, but it should be there somewhere.
Have a look in General - Applications Manager - All or Running or Disabled / Turned off.
If you have any app folders/trays in the app drawer / list I think it was in the Google apps folder originally.
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Just download the play store apk file. Do a Google search for play store apk file, which is the installation file for the play store; get the file and put it anywhere on your device. Now run the file and you will have the play store on your phone once again.

Using LG-E980 with Tapatalk
 
Look at application Manager, look for turned off applications, - This you can get it after sliding the all applications tab
You will find play store there, Turn on Again