how to access sys.user_history$ in aws oracle rds

Try,

begin
    rdsadmin.rdsadmin_util.grant_sys_object(
        p_obj_name  => 'USER_HISTORY$',
        p_grantee   => 'ADMIN',
        p_privilege => 'SELECT');
end;
/

Note: p_grantee is the schema or role that you want to grant the privilege to.

For more information on Granting SELECT or EXECUTE privileges to SYS objects please refer to the following link:

https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Appendix.Oracle.CommonDBATasks.System.html#Appendix.Oracle.CommonDBATasks.TransferPrivileges