P.S.: It is not a duplicated question, because I’m not looking to write contents in a file because it is already done, I’m looking to change a type of a file to be UTF-8, there is a difference in it.
How to generate the UTF-8 file and not ANSI. (Is not the contents).
For example, the most IDE have an option encoding, where you are able to modify the type of your file, but I’m generating a bulk from my database, and it generates a lot of individual text files, but the whole files is ANSI default.. I’m just looking for a function in php that make it possible to change the encoding before it generates the bulk.
If the source code help I can post it here. just let me know.
Thanks in advance.
EDITED
Follow a print of what I’m asking here.

When I generate the file “testecli01.csv” it always get encoding ANSI, whatever I do in my script it is always ANSI, and I need in UTF-8, just this. Is simple but I have no idea how to do.
If your 3rd party program "do not support files in ANSI but UTF-8" as you mentioned in a comment then most likely it’s expecting a BOM.
So strictly speaking your 3rd party program isn’t completely compliant with the standard because the BOM should be optional. ANSI is 100% valid UTF-8 and that is one of the main drivers of it. Anything that can understand UTF-8 accordng to the standard by definition also understands ANSI.
Try writing
"\xEF\xBB\xBF"to the front of the file and see if that solves your problem.