Text Variable with Customer Exit issue

Hello Experts,

I have Fiscal Week and Fiscal Year in selections screen, both will be calculated using Customer Exit variable. My requirement is to display text for column(WK "Current Fiscal Week Text Variable" Sales).

By default Current Fiscal Week and Current Fiscal Year are calculated and displayed in selection screen. I can able to display the text variable value for default value but in my requirement USER can change the Fiscal Year or Fiscal Week or both.

For this i have to write I_STEP = 2. In code can i use the following condition or how to write this condition and how can i take the input values. In loop can i use the code as follows.

IF I_step = 2.

LOOP at I_T_VAR_RANGE INTO LOC_VAR_RANGE

WHERE VNAM = 'ZCURRENTWEEK' or 'ZCURRENTYEAR'.

CLEAR L_S_RANGE.

any help to get the logic will be appreciated.

Thanks in advance,

Venky