how to use user EXIT_SAPLV50K_007 to idoc

hi,

my requirement is to use EXIT_SAPLV50K_007 for outbound delvery to transfer data from ECC to EWM.

in exit there are two parameters ET_EXTENSION1 and ET_EXTENSION2

to populate data into segements of idocs with my custom fields.

can any one please tell how to populate custom fields data into segements using  ET_EXTENSION1 and ET_EXTENSION2.

please answer .

Thanks,

phani