Regix in ruby on rails for adding "\n\n" " 2 new line" when i found "\n"

Question

I am new in regix and working in ruby on rails please help me out.

My scenario is :

alleyway\n behind the venue\n. The young agent never\n\n.

I have a paragraph. And i want to add \n only when i find \n. ex. in above sentence i want "venue\n\n".