The Unknowns Project lists 3 ways:
The most common uses of Recycle Unknowns are:
1) Select one that most closely meets your needs. For example you have a John Smith to enter. There is a profile in this category that has first name unknown, last name Smith and no other information - take it and use it, remembering to remove this category name.
2) You need a profile with an Unknown surname: select one and add your information, remembering to remove the category name.
3) You need a new profile but there is not one in this category that matches the last name you want to create. You may select one of these Unknowns, adopt it and change the name to suit your needs.