Ask your candidate how he responds to too much stress. Symptoms could be: getting angry easily, feeling irritable or tired, displaying less social behavior, drinking or smoking excessively.
Try and find the cause of your candidate’s stress. Encourage the candidate to keep a stress diary.
Encourage your candidate to engage in sports. They tend to relax and to increase stress resistance.
Encourage your candidate to ask for help when feeling stressed.
Evaluate with your candidate what can be the positive effects of having some stress (better achievements) as well as the negative effects of having too much stress.