Start date is in the past: today scheduling

Dear all,

How can I fix that error:

*Start date is in the past: today scheduling*

*Message no. C7030*

Diagnosis

The start date determined in scheduling is in the past.

In customizing, you have defined the number of days that the start date is allowed to be in the past. This number is exceeded.

System Response

"Today" scheduling is carried out.

how can i definea new number of days ???????????