Search Through Matrix Field
Please take a look at the docs there are so many examples how to search here at stack exchange and it's well explained in the docs. I posted the same answer multiple times within the last days 

entry.matrixField.search("mykeyword").all()


As I already said a few times too "looping through queries is still deprecated". Please fetch your results with .all() or .one(). There is no reason to fill your logs with deprecated warnings - you won't have any benefits