[cflsystems]

Use phpmyadmin to add another field, the table is probably xcart_products_lng_XX where XX is the language but adding it to one you will probably have to add it to all, this if you need it to show with different languages otherwise you can add it to xcart_products

Judging by the question though you probably want to get a professional to do it for you. Modifying the database without knowing what you are doing can damage it or lose all the info... and it is irreversible