To set a percentage-based admission control, follow these steps:

1. Log in to vCenter Server Web Client.
2. Click on Hosts and Clusters on the Home Screen.
3. Click on the cluster and go to the Configure tab.
4. Click on vSphere Availability under the Services section.
5. Click on the Edit button in the top-left corner.
6. Click on the Admission Control section.
7. Set the drop-down box to Cluster resource percentage and click on Override calculated capacity percentage, then set the CPU and Memory percentages:

8. Click on OK to apply the settings.