In the 'Keys' Screen

Tap the ↑↓ icon top right of the screen.

To delete a line select the recycle bin icon on the right hand side of the screen.
A pop-up box will appear to confirm you wish to delete the key, select ‘Yes Please’ and this will take you back to the previous screen
To return to the main Keys screen Tap the ↑↓ icon top right of the screen.