Step 1:
Use a triggering action (such as Form Submitted) to have the original opt-in send them through a Campaign or Workflow series, requesting that they confirm the opt-in. This can be a follow-up confirmation email, text, or both.
Step 2:
Within that communication, include a trigger link for them to confirm.
NOTE: Check out our tutorials on creating Trigger Links if you need assistance.
Step 3:
Set up a trigger action so that when the “Confirm Opt In Trigger Link” (whatever you named that which you created in Step 2) is clicked, the rest of the communications/interactions take place (i.e. any nurture campaign sequences, tag applications, pipeline changes, workflows, etc.)