Load balancing using service

service EMPL_HTTP1.NET is running on instance(s) EMPL1
Service EMPL_HTTP2.NET is running on instance(s) EMPL1

We were doing load testing yesterday and all the connections were routed to instance 1 as seen below.

  INST_ID   COUNT(*)
---------- ----------
         2         73
         1        301

   INST_ID   COUNT(*)
---------- ----------
         2         73
         1        347

 INST_ID   COUNT(*)
---------- ----------
         2         77
         1        436

   INST_ID   COUNT(*)
---------- ----------
         1        635
         2         72

Is there a way I can do load balancing specifically during performance testing?

Thanks