If things don’t work out
If you are not happy with a personal assistant’s work you should tell them as soon as you can. It is important to be clear about exactly what it is that you are not happy with and how you would prefer the task to be done. It is worth telling them verbally and noting it down as well.
Most work problems can be sorted out informally by discussing things with your personal assistant. If this does not work then there is a formal process you and your employee must follow as a minimum.
Further information is available at GOV.UK - dismissal or ACAS.