If possible, consider upgrading to a newer version of OCSM (5.x) or switching to NetApp Active IQ Unified Manager, which supports ONTAP 9.x legacy clusters better.
Unlike the modern HTML5 versions, System Manager 3.1.3 is a Java Web Start (JNLP) application. netapp oncommand system manager 3.1.3 download
After installation, launch from /opt/netapp/OnCommand_System_Manager/bin/ . If possible, consider upgrading to a newer version