To forgive means not to hold anger and resentments towards others, or accepting others without wanting to hit back. It is generally understood as pardoning others. But only the Law (judge) and God have the power to forgive people. So even Jesus Christ had asked God to forgive those who had crucified him, "Forgive them for they know not what they are doing." And he could say that because he had accepted them without holding any grudges toward them; he was not angry with them. When we humans try to forgive others, we find it very difficult to forget, which is the same as not forgiving.
It is usually the words and concepts we use, which themselves become obstacles in achieving our goal. This is particularly true in the case of 'forgiving,' which a person finds very difficult to do without forgetting. So I believe that we counselors owe it to our clients, and to the people, about being specific and clear about what we mean by 'forgiving.' So when we ask them to forgive someone, we should tell them that we mean 'giving up his resentment toward that person,' or 'accepting that person without holding any grudge, or feeling of hitting back, towards him.' Then our client would know what exactly he needs to do. And do whatever he can to avoid his anger and resentment. Of course if you really want to help him, help him with the therapy given in my book '12 Steps in a Day: The Lost path' or give him a copy of it.