Recently I was receiving this question so much from the recruiters: 'How to tell a recruiter you are not interested in a position?'Express gratitude for the chance while being straightforward about your choice to keep it professional and show gratitude.
"Thank you for getting in touch.
Although I'm grateful for the chance, I've made the decision to look into other choices that better fit my objectives. For any future chances, I would really want to keep in contact."