I'm trying to test the HA using my vCenter and when I contacted the provider of the service after implementing the HA I asked him if I can shutdown one of the hosts to test HA he told me that he can't do that
"you have to get access to iDRAC,
and to do that I have to “Enable OOB”
My question is I can't find iDRAC or how to enable OOB ?
so I need your help
This has nothing to do with vSphere. OOB means "Out-Of-Band", iDRAC is the DELL "LOM (Lights-Out-Management)" hardware / software. Basically it is a card in your server that has a separate IP you can access even if the host is powered down, it provides HW mgmt capabilities, console access, power operations etc.
I'm not sure where you get your hosts from but your provider should be the one organizing access to the HW or at least be aware of whether you do have any LOM.
If you just want to test HA, instead of doing a power cycle on the HW, you could also just crash the ESXi host, connect via SSH and run:
vsish -e set /reliability/crashMe/Panic 1
That will crash the host and everything on it, HA will then respond on the other hosts as configured.
If you would power down a host, how would you turn it one right now? This really is a question you will have to figure out with your provider anyhow. If you don't have control over your HW then this will be a real issue sooner rather than later.
This has nothing to do with vSphere / VMware though, if you don't know how to access iDRAC, ask them. OOB might refer to some functionality they provide, e.g. some mgmt interface that will setup iDRAC access for you.
As @vbondzio mentioned.
OOB has nothing to do with ESXi.
Your host should have two IP addresses configured. One is the management IP of ESXi and the other is your out-of-band (iLO, iDRAC, iRMC) address.
There should be a poweron function and hopefully a video redirection, where you can enter BIOS settings or boot manager.
If you have physical access to the server, checkt the cabling on the back. OOB has often a dedicated LAN Port with a wrench symbol.