code help needed

Dear experts,

Below is my internal table & values:

BELNR     REBZG    GLVOR       ZDAYS

101           501          SD00           35

102           501          RFBU           3

103           501          RFBU           4

104           501          RFBU           1

I need to write a code wherein:

1)  I take the REBZG as base i.e. 501

2) compare the GLVOR for SD00 value

3) update the ZDAYS lines with 35 (as for REBZG 501 and GLVOR SD00 the ZDAYS is 35, I want the same ZDAYS for all other lines of REBZG)

Request you to let me know the code.

Thanks in Advance.

Regards,

Syed