Hello @StephanieC4399 ,
By "reminder," are you referring to the automatic Resend to Non-Openers you'd set up for your email? That's an option that has to be actively turned on (including subject line and timing selection) on the scheduling page of an email.
If you need to turn off an RSNO that was setup for a campaign, prior to it sending
If that's not what you're referring to, can you elaborate a bit more on what reminder was inadvertently sent out?