Optiplex 5080 Micro Adding Boot Option for CD/DVD

Can I assume this is an external drive and not part of the 5080? And alternatively have you tried F12 at boot to see if the option appears in the one time boot menu?

If wiping the hard drive is what you want, you can select BIOS settings at boot and go to Maintenance.  You will find Data Wipe option, select to Wipe on Next Boot and restart.  Follow the instructions to complete the Data Wipe process.

If you do prefer to use DBAN, you can prepare a bootable USB drive from the DBAN ISO:

1. Download the Rufus USB Installer onto your USB flash drive: https://rufus.ie/
2. Click DBAN ISO for creating a bootable CD-R and choose Save. Save the file to your Desktop.
3. Run the Rufus application (double-click). If you see a message on your computer asking to allow the program to run, click Yes.
4. Rufus will find the USB flash drive. Under the Boot selection drop-down menu, choose Disk or ISO image (the default). Then click SELECT.
5. When the pop-up menu appears, choose the dban iso option. You can also choose to type “dban” in the Volume label field (so you can find it later in Windows Explorer).
6. Click Open.
7. Click START.
8. You will see a warning message telling you that all data will be destroyed on the USB flash drive. Click OK. Note: If you receive a message stating that the disk is in use, restart your computer and start the Rufus application again (step 5).
9. Once you create the Rufus DBAN bootable USB flash drive, click CLOSE to finish the process.
10. Restart machine with USB plugged in, select F12 at boot and DBAN USB will be available for selection.

Or you can attempt with CD/DVD boot by disable Secure Boot in BIOS settings, with the CD already inserted, select F12 at boot to access one time boot menu.  If the CD is available for selection, it can be used.  If there is no CD, you must prepare a bootable CD compatible in UEFI boot mode.  Hence the reason other suggestions were provided first.

@Chino de Oro​ I wiped the hard drive from the bios as dban could not wipe an SSD or GPT system, but now the hard drive password protected and I don't know the password, how can I bypass the password without knowing it and without an operating system because I wiped the operating system but it still has leftover data cuz it's locked and I can't install a new operating system.

Probably not the workaround you're looking for, but it could  be worth a try.

Install a new SSD/HDD in the 5080.  Install Win10.  Connect externally the HDD you want to install RHEL on using an external HDD dock or enclosure.  Go into Disk Management in Windows.  Find the drive you want to install RHEL on.  Reformat the drive.  Even if it's already formatted with NTFS file system and GPT partition scheme, doing so again will wipe the drive and wipe the password.

@Domoi​ go back into BIOS settings, select to change HDD password.  In the old password space, try "password" as password, just leave the new password space blank.