How to replace a specific letter on p?

Question

Character encoding

Cheerful day.
I have such a situation, I struggled with the encoding on my script, everything was decided in words in .htac by the command to force the installation of the encoding on the files of the formats that I need. As a result, everything is displayed as it should, BUT one problem remains: When you fill out any form and send it, as a result, if the letter "I" was large in the form, it is displayed like this - �? . That is, in the profile editing form, for example, I wrote "Ivan", which will be displayed as a result as �?van. As I see the solution - a script that will automatically change "�?" on "I", who's to say?