I volunteer at my church and have done these courses (a few times, as they have to be revisited after a few years to update)
A lot of it I do already know, but there is always something new in there
You just never know when it will come in useful, and if most of your customers are elderly, they can be more susceptible to financial abuse, problems with dementia and many other mental and physical health issues
If you like helping people - which I am assuming you do as you volunteer - I cannot fathom why you feel unable or unwilling to give a couple of hours to do this
Quite often, it is a legal requirement, so they have to ask you to do it. Even if not, it can be a spiritual one and if not that - a moral one. It's about showing love and care for others
I don't know if you are a Christian or not, but something we spoke about in our church when discussing safeguarding is what would Jesus want us to do.
We decided safeguarding definitely comes under the heading of 'love your neighbour as yourself'
We should actively want to do it, because we should want to look after each other as much as possible
Please consider it prayerfully; then either do it willingly from the heart, or accept you need to step down from volunteering graciously