How do I use the viosupgrade tool to upgrade to VIOS 3.1? Here's one example of how you could use this new tool to upgrade: https://www.ibm.com/developerworks/community/blogs/cgaix/resource/viosupgrade_altdisk_v3_GA.pdf

This example shows you how to use the viosupgrade tool to upgrade to 3.1. 

https://www.ibm.com/support/knowledgecenter/en/POWER9/p9hcg/p9hcg_viosupgrade.htm

https://www.ibm.com/support/knowledgecenter/en/ssw_aix_72/com.ibm.aix.cmds6/viosupgrade.htm

Please note, that this process is an upgrade NOT a migration. It is essentially a fresh install with a viosbr restore. It will require some reconfiguration afterwards.