I figured it out with the help of the discord channel. The documentation as usual is terrible. What you need to run in powershell command line is this:
& .\UnrealEditor.exe “Path/To/UProjectFile/Here.uproject” -run=WorldPartitionConvertCommandlet “MapName” -AllowCommandletRendering 2>&1 | Out-File .\output.txt
NOTE: MapName does not need to have the .umap extension specified.
The full command I ran on my local computer for one of my projects:
& .\UnrealEditor.exe “E:/Repos/Raevin 5.0/Raevin.uproject” -run=WorldPartitionConvertCommandlet “CtrlRigMapTest4” -AllowCommandletRendering 2>&1 | Out-File .\output.txt