Mastodon has a post editing feature which lets you make changes to your posts after they've been published.
Here's how to edit:
1. Go to the post
2. Click ⋯
3. Click "Edit"
4. Make the changes you want (including adding or removing attachments, or adding alt text or polls)
5. Click "Save Changes"
⚠️ NOTE:
To prevent abuse, every edit sends a notification to everyone who has interacted with post.
Editing poll options resets poll votes to zero without warning.
You cannot edit post visibility.