Backup help

Someone I know lost their backup of our chat. Would it be possible to save only a backup of ONE CHAT (between them and myself, from an iPhone, (including ONLY that chat, none of my other chats on WhatsApp, or I could potentially delete the other chats for this purpose?) and then somehow install it to their phone/software directory but from their user account?? I am guessing if it is tied to phone number it wouldn’t be possible but if there is a way to simply install files to the software directory, maybe? Could there be any way at all to do this or in some other way restore their our chat so they are able to go back and read past info?