@salderete here are a bunch of links I look at, I didn’t look at them, but I searched “how to add a field to SSRS report” in the search bar and these are some that looked ripe:
SSRS - Add Field to Report - Epicor ERP 10 - Epicor User Help Forum
SSRS Add New Field to Report - Epicor ERP 10 - Epicor User Help Forum
Add a field to SSRS RDL report dataset - Epicor ERP 10 - Epicor User Help Forum
SSRS Custom Report Help - Kinetic ERP - Epicor User Help Forum
ARForm modification - Epicor ERP 10 - Epicor User Help Forum
Trying to modify RDD for PackSlip report - SSRS - Epicor ERP 10 - Epicor User Help Forum