替换方框字符

I am trying to replace some data from a database which has a special character encoded Ä which is the letter "č".

If i target the "Ä" and replace it with str_replace with "č" it works but the blank square is left, since it's not fetched on replacing, I have no idea why.

How to replace this character ?

Here is a image since, I cannot paste that square box here:

Thank you