Hi @cynthia,
adding to what @Bobi N. said you could also just schedule these campaigns. What worries me a bit is that you're mentioning you want to send it to people who signed up a year ago.
If you haven't send them any emails in between it might be unexpected for customers to get your email out of the blue and this in turn can cause people to mark emails as spam or unsubscribe.
Whatever you do keep a good view on the open, click, unsubscribe, bounce an spam rates.
Sending a campaign might be best way to do this and scheduling them instead of adding it as a Flow (preference) and I would create a segment to exclude all people who haven't opened or clicked or done anything or had a soft bounce i.e. in the last 3 emails.
Hope it helps,
Omar Lovert // Polaris Growth // Klaviyo Master Platinum Partner
We help with e-commerce growth through CRO, Klaviyo and CVO