An affirmation is used in your own language. The aim is mostly to find awareness, insight, self healing or enlightenment with positive affirmations to influence your system towards a positive attitude in a cognitive way. There are many ways to find YOUR affirmation.
I personally started with Louise Hay Cards. After that I read her book ‘Heal Yourself’, in which you find affirmations for lots of body reactions.
Another way is to follow the Chakras. Every Chakra (see chapter CHAKRA) has a topic and a task, so there are quite a few affirmations you can use to revitalise or align your chakras (see also Chakra Workshops and Chakra Meditation).
It is possible that the affirmation you chose changes during the meditation or that another related topic occurs … trust your intuition and follow the affirmations down the rabbit hole … this might bring back a long hidden gem.