Use tcode SMGW via menu Goto >Expert Functions> External Security> Maintenance of ACL Files.
https://wiki.scn.sap.com/wiki/display/SI/RFC+Gateway+Access+Control+Lists
https://wiki.scn.sap.com/wiki/display/SI/RFC+Gateway+Access+Control+Lists#RFCGatewayAccessControlLists-secinfo
SAP Note 1850230 – GW: “Registration of tp <program ID> not allowed” [VIDEO]