I'm not sure how to fix it so that it will become mobile friendly.
No way for anyone here to offer any specific advice or help without seeing the site. Depending on the problems, it may be outside the scope of these forums - as extensive CSS work can be involved - from what you say about TK's response, that may well be the case. Certainly unfortunate. Maybe you should set up a duplicate test site and try another known-to-be-well-coded responsive theme. There are many...