User Exit (steps)

Hi,

I have a variable (customer exit) in a query: FINIEXT:

- Characteristic is a date

- Ready for Input

- Interval

I want to change the interval of the data of the parameters enters:

Example:

User parameter entry : 01012009 -01012010

I want to change in the STEP 2 of the USER EXIT to : 01012009- 31129999.

But when I execute the query, STEP 2 is not stoped. Only step 3.

Any idea?? I have to do it in STEP3???