You can stuff around and go site setting > site contencts  > recycle bin > blah blah blah click click click or just punch in the url to correspond to your tenancy.

** has to be turn on in the first place though and you have to be the poor admin that has to fetch that accidental deleted file  **

https://your0365Tenancy.com/_layouts/15/AdminRecycleBin.aspx?view=5

 

select file > Right Click  > restore