Create a new record in S_ACT_ORG by using EIM

Hello! We are running on Siebel 21.12. Our initial implementation used 1:M relationship between Account (source column: ROW_ID) and Action BC (destination column: TARGET_OU_ID), however, we have changed this relationship to M:M (intersection table S_ACT_ORG). Now we need to run a conversion script in order to make old activity records to be displayed under accounts. We've chosen to make the update by using the EIM, however we are not experts in this area and need some guidance how to perform this in the best way...

We've already found that EIM_ACTIVITY1 table can be used to export data from S_ACT_ORG, however EIM_ACTIVITY1 doesn't contain any column that could be matched to TARGET_OU_ID. Can this mapping/column be added to EIM_ACTIVITY1?