To bring up BIOS settings, you will need to start tapping on F2 or F12 (boot menu) as soon as you see the Dell logo.  You keep tapping (not holding the keys down) until BIOS setup screen appears (F2) or a message one time boot menu (F12) following by boot selection option. For better control and select preferred boot device, using F12 so you can select to boot from the DVD, the rest will be just like you already guessed.  Other information to note, if you are installing operating system (Windows) under legacy mode, your hard drive may be limited to 2tb due to formatting with MBR.  Your DVD may contained an older version of Windows 10, using a USB drive created by Windows Creation Tool may help to obtain the most recent, latest version.  
Hi Gang I have a genuine Dell Disk (Full Install Version) W10 Pro ... I forgot the 'rule of thumb' regarding successful format using a Dell Disk (Full Install Version)? Is it necessary the 3620 case needs to have the 'Dell Label' affixed to the case in order for the system & drive be able to recognize & boot off the disk? There's an original service tag attached but no Dell OS Label .... Thank You   
Formatting 3620