Choose to Forget internal storage, how to recover I'm using Moto G 2nd Gen with Android version 6.0.

I was using external SD Card as Internal storage and I guess it has encrypted the card.

Recently, my phone started to work abnormally. It randomly fails to recognize the storage. After a device reboot, it would work for sometime and fail again.

In the "Storage &amp; USB" settings menu, I clicked "Forget" on the external SD card.

Then I realize I cannot access the data from my computer using SD card reader. 

How can I re-plug the SD card back as Internal Storage without formatting again?
I can't help really, but I sympathize.  One commenter said "It's your fault".  No it's not!  Some stupid moronic programmer decided some idiotic protocol was required and the Moto G 2nd Gen quit reading any Micro SD card regularly, that is, encrypted for Andoid.  I had the exact same problem.  After upgrading to Marshmallow the damn thing quit reading my 64Gb high speed card.  So I dropped down to a 32Gb thinking it was compliant with manufactures specs.  Nope the 32 Gig failed just as much.  It would read the card for about 2 minutes and then stop.  I couldn't make a backup of the card, so you did the right thing.  Just start all over, format and get the BS encryption off your storage device.  If you ever format it again with Google encryption, well, then it's your fault. :)

Now root your Android roll it back to the previous build and you'll be able to shove a 128Gb Micro and it'll read it just fine.  Then you give Google a big FU for wrecking a perfectly functional phone.