Dear Mark
Are you a customer or BP? If the former, you should ask your local IBM i BP do the proposal for you.
But if u r a BP, first you need to have an active SWMA on the source machine (P9) to be eligible for the license transfer. If you no longer have an active SWMA on P9 machine, then paying for SWMA renewal + license transfer charge MAY cost similarly or even more than buying subscription license on the new P11 machine.
To do the license transfer, you need to have to manually build a base config of P9 source machine's HW and SW as the starting point using e-Config tool. In the HW part, you need to specify accurately the machine type + model of P9 server while all other HW details do not need to be accurate as they are not use in the upgrade process. You may even enter the base minimum HW config of the P9 server if obtaining the full accurate HW list will take big effort. But the SW part need to be entered accurate and it must include a SWMA product feature. Once you manually build this (or luckily can obtain the list from IBM, but mostly it is not accurate but it reduces your task from having to start from scratch ), you save it as a CFR file and use it as the input to e-Cinfig to run machine upgrade + License transfer.
I attach herewith an IBM i License Transfer FAQ file which explains in some details what to specify in e-Config tool to do the transfer in different scenarios. Keep in mind the file was from 2016 and what you see in current e-Config tool may look differently or even partly changes.
For more info on this, go to this URL: IBM I License Topics at https://www.ibm.com/support/pages/ibm-i-license-topics and scroll down to the section IBM i Processor and User Transfer.