Legacy asset creation in AS91

Hi

We are trying to upload the legacy assets using transaction code AS91. We are fine with all the fields but we want different depreciation start date for different depreciation area. Say for example for depreciation area 01 depreciation start date should be 01.04.1997 and for depreciation area 30 depreciation start date should be 01.04.1992. But I could able to enter 01 depreciation area start date but not for depreciation area 30, because it is gray out. Can you please tell me how to open depreciation start date field for all depreciation areas.

Regards

Padma