If you want to set the RoleName based on the value of Group, then I would do the following. Assuming that the Group value is of String.
I named My example entity DataImport
By the way, if you want to set the USERROLE for accounts in order to login in. Take a look at this learning path to understand how ACCOUNTS can be created automatically; https://academy.mendix.com/link/module/325/lecture/2498/8.7.1-Creating-Accounts