In the mobile app you can add items via search.

Simply search for the item you are looking for. If the item you're searching for isn't found, you will see the option to "create one here". From there, you can give the item a name, a serial number, add it to a group if you require, and add the date of manufacture (DOM) and date of first use (DOFU).

Take a look here if you’d like step-by-step instructions.