EPM input form help

Dear Expert,

I have an issue when creating input form like this.

I have a dimension B overides base on property C( C = B) of A dimension. it means A have 1-1 relation with B by property C. But data of customer 1 A  dimension member has 2 B dimension. So I cannot maintain property C of 1 A with 2 value.

How can I solve this issue?

please help me.

thanks so much