In EXSI's web interface, log in, go to the home page. Click on Actions > Services > Enable Secure Shell (SSH).
SSH into server
Run this command to list the disks that are attached to the ESXi host:
Find the disk that you want to map to. It should start with t10
Make sure there is a SATA device on the server, if not Add other device and select SATA device
Next "add hard disk" and select existing hard disk. Then navigate to the VMDK you just made, and select it. Make sure the Controller location is the new SATA controller made and that Disk compatibility is Physical.
It should look something like this: