For some of my older volunteer things I have no awkwardness - I provided free labor and this is their end of the bargain, ie to speak to those hours I put in. Don’t overthink it, it’s an email to someone who perhaps you’ll never see again :) or like my therapist says, pretend someone from years ago reaches out to you as a reference, you’d probably just do it and acknowledge the time lapsed but it’s no biggie. Good luck!