Responding to assistant advice

In almost all my games including the one's I'm winning the assistant states under statistics that we are doing poor at tackling, I play a 4-4-2 anyone now what I should change tactically to improve this?

Get better defenders; ones who can tackle. I'm not sure there is much you can change if your team are just tackling poorly. Work on more defensive training or get better players.

Possibly saying that you are disappointed with their performance in the half time team talk could work. Of course that is going to be inadvisable if the team is winning and playing well. Players that are told they are playing poorly when they are not can get annoyed.

You could look at some specific training instructions for your defenders, such as don't dive in to tackles.

I think it's more a note for later than something to change in the match. It will give you a reason as to why you are leaking some goals and give you something to think about.