Change the field kna1-begru with an user exit

I want to change the field kna1-begru with an user exit for XD01 transaction.

I need to take the value from knvv-vkbur and put it on kna1-begru. I have tried with the user exit EXIT_SAPMF02D_001, where I can read knvv-vkbur, but I can't modify kna1.

I am searching for a user exit for XD01 where i can modify kna1.