The "System" password is a BIOS-level password. Boot the machine and press F2 (usually) early in the boot sequence to go into setup. If you can boot without being prompted for a password before the OS loads and see/access all the BIOS setttings in Setup, there is no password set in the BIOS and there is no need to set a jumper to clear the NVRAM and make it forget it.
Resetting any BIOS password(s) will make no difference to any OS passwords (although resetting a drive encryption password, if set, would basically scramble the drive and require you to re-install the OS).
Not all Dells come with reinstallation/recovery media. The cheaper models, especially, tend not to (it's a $20 option). But it probably has a recovery partition on the machine from the factory. Pretty sure you can boot/reinstall/repair/reset to factory defaults from this.
https://www.dell.com/support/article/us/en/04/sln288623/what-are-the-system-recovery-options-in-windows-7?lang=en
The easiest way - especially if the reocvery partition isn't there or usuable - or someone replaced the drive - is to buy the Dell media. It's a few bucks, and the correct one for the machine will come with all the correct drivers for that hardware pre-loaded.
https://www.pctechbytes.com/dell/order-recovery-disks-from-dell/. Sometimes available on Ebay for about the same money as a coffee. Or ask the original owner; he might still have them.
If the case still has the Windoze COA sticker on it, you have a Dell OEM Windows license. Download a generic Win 7 ISO compatible with license (Home, Professional etc). These images are still hosted by Microsoft/available from their web site. Use the key from the COA when prompted to license it after installation.
Then, for best results, go through and install the Dell chipset/network/audio/graphics/everything else drivers. Freely downloadable from Dell, together with service/owners manual etc.