How to add data to new field in data dictionary

Hi All,

I have added a new field to a ztable as a key field. Now i want to add data to this field. I went to sm30 and saw all the existing records.now i want to add the data to the existing record to the new field.but the new field is in the grey mode which cant be edited.Please help how to add data to it....

Thanks

Phani...