Steps for adding more CPUs in VCMP guest

There are 2 ways to do it...

Per the manual...

1. Log in to the BIG-IP Configuration utility on the vCMP host, using the BIG-IP system's primary management IP address.
2. On the Main tab, click vCMP > Guest List .
3. View the graphic to determine the number of unused cores available on the system.This tells you how many cores are available to add to the guest.
4. In the Name column, find the name of the guest that needs additional CPU cores and confirm that the Requested State is Deployed.
5. To the left of the guest name, select the check box.
6. Click the Disable button.The guest state changes from Deployed to Configured.
7. Important: It might take a few minutes for the guest state to change to Configured.
8. Once the screen shows that the guest is now in the Configured state, click the guest name.The guest properties screen opens.
9. From the Cores per Guest list, select a higher number of CPU cores.For example, if you currently have two cores allocated to the guest and you want to add two cores, then from the Cores per Guest list, select 4.
10. Note: Do not select a value that exceeds the total number of unused cores available for use on the system.
11. From the Requested State list, select Deployed.
12. Click Update.The Guest List screen opens again and you will see that the guest state is changing.
13. Important: It might take a few minutes for the guest state to change back to the Deployed state.

https://techdocs.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/vcmp-administration-appliance-13-1-0/6.html

Or you can go can click on the guest itself and set it to Configured in the dropdown. Either way way will disable the quest so you can add the cores to it.