transform script target field

Hi, I have a scenario where if I get any value that doesn't exist in choice list (target table field is a choice list where label and field = ABC). The issue is how to set the target field value to the default value as 'ABC'. Please help me with this. Thanks.

If(source.u_company_name == 'ABC' || source.u_company_name == 'DEF'){

ignore =false;

} else {

target.u_company_name = 'ABC';  // not able to get this set

ignore =true;

}