Here is a sample template you can use to write an acknowledgment letter about work immersion.
To [Recipient name]
Dear, [Recipient name]
This letter is to offer my gratitude for accommodating me in [Name of company] as the skills that I have acquired from this work immersion training is extremely valuable. The practical, as well as technical skills that I have learned, will prove to be beneficial for my future endeavors.
I would also like to thank [Name] for helping me become familiar with the work processes of [Name of company]. Your patience and wisdom is invaluable to me and I am eternally grateful for this experience.
Thanking you again for your constant support and guidance.