See the prerequisites listed under User-Specific Selection Variables.
To create a user-specific variable for a variant that already exists:
...
1. In the initial screen for maintaining variants, choose the appropriate variant.
2. Select the Attributes field.
3.
Choose Change.
The attributes screen
for the selected variant is displayed.
4. In the Selection Variable column, press F4 and choose a type of selection variable. The display window shows the possible types for the selected field.
5. Choose Type B for user-specific variables.The Variable Name column is filled automatically. You return to the attributes screen.
6. Save the attributes.