You will have to click on the 
button present at the top right-hand corner of the Punch list dashboard to open the Manage Stamp pop-up box.
This is shown in the screenshot below,
You can create stamps from this pop-up box and also edit & delete existing punch stamps. But you cannot delete punch stamp which are currently being used, that is, currently associated with a punch.
If you enter 'FC' in the text box named Stamp and enter Floor Cleaning in the text box named Stamp Title and click on the 
button then a Stamp will be created and will appear as,
From Manage stamp pop-up box you can create multiple stamps.
Note: A maximum of up to 3 characters can be entered as Stamp initials like FCB for Floor Cleaning of Basement.