Your friend has not fared well in the recent examinations. Write a letter to him/her expressing your concern. Give him/her some advice to how to score better marks and offer to help him/her to improve his/her performance.
55 Diamond Avenue
14th March, 2019
I received your letter yesterday wherein you have mentioned that you have not fared well in the examination.
I can understand that you must be under a lot of stress but this is not the end of everything. We know that hard work is the key to success and we can achieve every goal with hard work and patience. Failure is the stepping stone to success. You must not lose your heart. It is not the time to brood or be anxious. You should make a timetable and strictly follow it. Work on your weak subjects and try to get a good score next time.
I hope you will pay heed to what I have written and try to put it into action. I expect a positive and encouraging response from your end.