(Swipe from left to right until theMailboxeslist is visible.)
TapDoneto stash your selections and return to theMailboxesscreen.
Each item you selected appears at the top of the Mailboxes list.

The mailbox or folder is not deleted.
It is still available in the applicable account section further down the screen.
All Apple Mail folders can be added to the shortcut list.
The other folders for each email provider are located further down the screen.
Rearrange Entries in the iOS Mail Shortcut List
Swipe from left to the right until theMailboxesscreen appears.
Drag the folder to the desired position.
Release your finger and the folder.