Sale order : new variant determination after change configuration (MRP3)

Dear Gurus,

i have the following scenary :

1. Create Sales order with configurable material (values : A + B)  (VBAP-CUOBJ)

2. Create variant material (configurated with the same configuration (MARC-CUOBJ)

3. Now i need to determinate material variant in sale order in order to substitute configurable material with variant material.

Now a use a custom BI in sales order going to configuration data of the sale order position , but i would like to now if there is a FM for this activity or a standard report which run a new determination variant in sale order

Thanks a lot

Daniele