If you have a paid plan you can always set up the Auto resend to those that did not open the initial campaign before you send it. Enable it in the first step of creating a campaign.
Once you enable the “Auto resend” feature, you will have the option to set a delay from the initial campaign and the follow-up email name.
If, for any reason, you did not set that up, do not worry, there is an easy workaround for it.
Go to Subscribers -> Advanced filter. Choose groups that you selected as recipients for your initial campaign. Then add another condition, “Did not open,” and choose the name of the campaign.
Then click “Save as new segment” and type in a name for it.
Now go to Email campaigns, click the arrow next to your initial campaign and choose “Duplicate”.
After the copy has been created, click “Edit”, and apply changes to the settings and the campaign itself if you want to. Once you reach the Subscriber section, find and select the segment that you have created. Now finish the necessary steps for sending the campaign as you normally would.