Once a campaign is sent, changing the content is not possible. Moreover, it's not possible to unsend a sent campaign.
If you'd like to rename a sent campaign, you can do so by:
Clicking the More button on the right-hand side of the sent campaign
Selecting Rename from the dropdown
An alternative to making changes in a sent campaign is sending a follow-up email to your subscribers. It can simply be a heads-up correcting the mistake on the first campaign. Trust us; your subscribers might even appreciate you for making a follow-up!
🔗 Changing (wrong) links is an exception, as you can edit URLs on sent campaigns.