There may be times when an individual is unhappy with decisions that were made on their behalf or with the choices that they were offered. It may not be within your power to change this, but there are other things you could do to help the individual with their decisions.
Primarily, you should remind them of their right to complain and support them in following the complaints procedure laid out by your workplace. Through the complaints process, you may be able to improve the choices an individual is presented with, and improve their care by extension. Remember that the individual always knows what is best for their care, and if they are unhappy they should be supported in their right to complain.