To write a thank you letter to persons who donated something to you, You can follow the below steps:
1- Start with warm greetings and wishes for his life and family.
2- Remind him about the donation case and how exactly you felt once receiving his donated item.
3- Tell him how this item means a lot to you and how much you appreciate his good initiative.
4- Also mention how much this donation improved our life.
5- Thank him again and wish him best wishes that may let him feel how much he affected or life positively.