Follow the Simple Steps below :
1. Login to your Gmail account
2. Go to TRASH folder / Left Column
3. Below Inbox - More - click Trash ....
4. Select the Message / Email
5. On top click the Move to folder
6. Select inbox
7. Now your message / email will move to inbox .
!important - After every 30 days Gmail automatically remove or empty the trash folder...so try to restore before 30 days.