Can’t frog yarn - pulled through loop

[MadelleB]

I need to frog back some of my project to get the working yarn back, but I’ve cut the yarn and pulled it through the last stitch. 
 

I can’t work out how to thread it back the way it came so that the yarn is “froggable” - essentially I’ve “finished off” the yarn and need to undo it - please help! 
How do I rethread it through the previous stitches to make it a live stitch again?

 

[Granny Square]

So you have only just pulled it thru the last stitch, no extra weaving in? 

Try this first: GENTLY pull on the end.  One of the loops of the last stitch should visibly pull tighter.

If that fails, gently pull a loop in that area a little at a time to see which one loosens up; maybe use a tapestry needle, or the hook end of a smaller hook, and sort of 'encourage' one of the loops to loosen up one by one until you find the right one, then you should be able to pull it thru.