I have just outlined and flooded my cookies and left to dry overnight, the next day I found that my cookies had gone soft, how can I overcome this, maybe my flood icing was too runny, I don't know, grateful for any feedback please
Royal icing will soften the cookies. If you are wanting a crisp cookie as your final outcome maybe you could bake them a little longer than normal so they start out crisper - possibly this would negate the softening and leave you with the crispness you would like!
I'm just a hobby baker so I'm sure you'll get more answers from more professional sorts :-) However, I have had this problem before. After you outlined and flooded them, where did you put them? I bake 3/8" cookies because it happens less the thicker they are (at least for me) and leave them to dry overnight under an oscillating table fan, right out on my table (on cooling racks). I found, that if covered before completely dry (RI), it was like having my cookies in a terrarium...the humidity in the air made my cookies soft and my icing had a hard time setting all the way through. I keep them under a fan until 100% decorated and then package after thoroughly dry. I do live in a sub-tropical environment...even last night, I notched the a/c down a couple of degrees to ensure the very high humidity we are experiencing would not effect all the hard work I did yesterday.
Agree with Debbi - work in an air-conditioned environment and don't cover the cookies until completely dry. I don't usually dry under a fan, just at room temp or in a dehydrator for certain small areas. I rarely have sogging problems, but I bake my cookies crunchy to start (as I like them) and do all of the things just noted. Too loose icing will take longer to dry and can also exacerbate the sogginess issue. So you'll probably want to play with a few factors.