As you create your campaign and decide that you want to resend the same campaign to customers who didn’t open it initially, follow the below steps:
When you're on the Schedule step, select the relevant option of the dropdown by the Repeat Send:
1 : Will send one reminder campaign.
2 : Will send two reminder campaigns.
3 : Will send three reminder campaigns.
From the drop down, select the number of days from the Interval (days) dropdown after which you'll send the campaign reminder.
Proceed with your campaign scheduling details.
Once you're happy with the campaign setup, click Submit.