Open Gmail
Click the Search mail bar
Type `in:all` to view all mail, including archived messages
Type `in:archive` to search archived mail
Enter sender name, subject, or keyword to narrow the search
Open the archived email from the results
Click the Move to Inbox icon to return it to your inbox
On mobile, open the Gmail app
Tap the Search bar
Search using `in:all` or `in:archive`
Open the archived email
Tap the More menu
Select Move to Inbox