Go to LiteSpeed admin interface and adjust the following:
Configuration -> Server -> Edit -> "Enable LVE" = "Yes" -> Save
If you are using CageFS then select CageFS there.
To enable PHP Selector with LiteSpeed you have to adjust more settings inside admin the same interface. We have a detailed instructions about it here.
Another peculiarity you need to have in mind when switching to LiteSpeed is that EP limit can be counted differently with different Process Modes. You can read more about PHP Process Modes in LiteSpeed here. The default PHP Process Mode is ProcessGroup Mode. This ProcessGroup mode provisions an additional parent process for each process group user. With this mode, the parent processes are counted as Entry Processes (EP) and all other children are counted towards the Number of Processes (Nproc) limit. In order to limit entry processes, you can also use PHP suEXEC Max Conn value.