How to change encoding from iso-8859-1 to windows-1251?

Question

PHP

The situation is this: I get a query that the user enters into the search bar and apply the preg_split function. After that, the word encoding changes and, judging by the mb_detect_encoding function, to iso-8859-1. Is it possible to somehow change the encoding to windows-1251?
Tried iconv doesn't work
I also read that mb_detect_encoding can incorrectly determine the encoding, while how can it be determined correctly?
Gives such a character �, I read that it is UTF-8, but when applying iconv, the string becomes empty

Answer 1

The iso-8859-1 encoding cannot contain Cyrillic characters, so it is not possible to recode from it to windows-1251. Please provide an example of what you see.