Here you can read how to resend a campaign to contacts who have not yet opened the email. You can also incorporate this into an automation. This article explains how.
Create a new automation and choose a start trigger.
Add an email.
Add a wait step, for example, of 1 day.
Add an if/else step and fill in the condition as: 'Has opened - Campaign'. You can now select the previous email.
Has a contact opened the email? Then they will follow the yes path (in the example, a wait step and another email are added in this path).
Under the no path, you can add the first email again so that contacts who have not opened it yet receive it a second time. To do this, hover over the email, drag it to the correct position, then choose ‘Copy single action’ and click ‘OK’.
After this, add the 'Go to’ step to bring the paths back together.