Install Full Disc Version Windows 10 Pro

"you will have to purchase another license from MS"

How difficult is that? Its my understanding Microsoft doesn't sell Licenses for W10 Pro anymore?

Its also my understanding that I could use a creator tool to make disc (which also seems vague).

I think I'd rather just buy another GENUINE Full Install Disc which are STILL available. Note the GENUINE product key and License Number - Sample image:

Re:  Could someone please provide the Key Prompt (booting off the disc set in Bios)?

To boot the disc, just simply insert it into the machine's DVD drive.  Tap F12 key at power on to select the disc from one time boot menu.  No BIOS settings is necessary unless the system does not recognize the optical drive.  Sometimes, system will automatically boot the disc when there is no other bootable device present.

As for the license concern, the 3620 may already has one embedded.  If the Windows installation went through without asking you to enter key, then it found one and will activate when system is online.  If the installation asking to enter key, just tick the box don't have key and you can purchase one to activate it later.