You can express your gratitude to the trainer by sending a thoughtful message. Here's an example of what you might say:

"Dear [Trainer's Name],

I wanted to extend my sincerest gratitude for your invaluable guidance and patience throughout the computer training in digital transformation. Your expertise and support have not only enhanced my understanding of the subject but also made the learning experience truly enjoyable. Thank you for your dedication and for being such an inspiring mentor.

Best regards, [Your Name]"

Feel free to personalize this message to reflect your own sentiments and relationship with the trainer.