The first thing to do is to give the student confidence, regardless of his difficulties he must understand that he has all his chances of succeeding (even if he is convinced otherwise;)). The problem must then be identified (find the cause and the nature of the difficulties) in order to best adapt to the student's needs. The rest of the work consists of taking the rest of the course point by point if necessary to ensure that everything is mastered (with exercises, training topics). The steps vary according to the needs of the students, some will simply want to deepen the subjects already mastered.