Dear Mr or Ms,
It is wonderful to see such a commendable initiative on your behalf to encourage people to conduct voluntary service to benefit your hospital in our community. While the advertising does not specify the type of unpaid job for which you are looking for assistance, I believe I could still be a part of this wonderful project since it would allow me to help sick people in the hospital while also expending my leisure time to do something good in my ability for other people in society.
Furthermore, this free job experience would allow me to acquire something valuable that I could utilize for the rest of my time. Again, I appreciate that you have not requested that I fill any particular open employment positions in your posting, but I would be pleased to support a nurse or a doctor in monitoring patients' temperatures and check their blood pressure, to name a few ways I may assist them.
So, please consider me for the role of 'unpaid worker,' since it would not only provide me with valuable experience in the future but would also allow your regular personnel to lessen some of their excessive burdens. By the way, I am available to work Monday through Friday from 4 p.m. to 7.30 p.m.
I am looking forward to hearing from you.