This tested on ESXI 6.5 and I’m sure it not much change since.
Download Esxi VIB version you need from Dell site and also the Windows ver need
Download WinSCP and Putty. You gonna need it.
Enable SSH on esxi
In esxi go to service and SSH, click Configuration Tab\Security Profile\Properties Set to Start Automatically.
Open WinSCp and connect with ESXI and copy downloaded files , I mean VIB file to /var/log/vmware
Then open putty and connect with ESXI and run the command and use your ZIP file name
esxcli software vib install -d /var/log/vmware/OM-SrvAdmin-Dell-Web-8.1.0-1518.VIB-ESX60i_A00.zip
Now you can install open mange on the server OS and connect to hardware via Dell open mange.