As of now, PI 3.1 on Gen1 is not supported.
Regarding taking backup and restore, we can't do directly in PI 3.1. We would need to move to PI 3.0 and restore it and take the PI 3.0 backup and then finally restore on PI 3.1
We have PI 3.1.3 available now. You can install Cisco Prime Infrastructure 3.1.3 Maintenance Release on Cisco Prime Infrastructure 3.1, 3.1.1, and 3.1.2 versions.
Release notes :- http://www.cisco.com/c/en/us/td/docs/net_mgmt/prime/infra...