If Dell says the the system originally came with Windows 7, you might want to check and see if the system even supports Windows 10 (check the support page for Windows 8/8.1/10 drivers for download).
The problem you might run into here is sometimes, you cannot just get a generic Windows OS and install it on a Dell laptop. Sometimes, the laptops require custom settings within Windows in order for it to run stable on the system. This is why they provide you either with a Recovery Disk or the means to create a Recovery Disk.
The next problem is that if this WAS a corporate system under volume licensing, then the recovery disk option is probably through the original company (though asking Dell was an option).
What I would TRY and do in time for Christmas would be to use the
Windows 10 Media Creation Tool to create an ISO for your laptop. If you're getting a Windows 10 Pro for Workstations license, then be sure to follow the pertinent instructions listed on that site. You'll skip the activation process until you get the valid Windows 10 product key. Format the drive and install the OS from scratch.
You can run a non-activated Windows 10 machine (minus some personalization functions) without issue, at least, you can with Windows 10 Home, and just hope the installation works on
your laptop.
If that doesn't work, then hope the license key you get from Newegg allows it to work.
If not, then your last option would be to work with Dell (if you can) and get a Windows 7 recovery disk from them (at your cost).
Just a heads up about working with Dell. A number of years back (less than 10), my nephew came to me with computer problems and asked me to look into them. I did everything I could think of and then decided to just do a recovery. My nephew didn't have a recovery disk and I couldn't create one from the recovery partition.
So I contacted Dell. I gave them the Service Tag and they asked what company I worked for. I told them this was a used personal computer that my nephew had purchased and they told me that I needed to have what amounted to a written transfer of ownership letter from the original company. Of course, I couldn't provide them with one, because my nephew bought it from a guy he knew, who bought it from a guy he knew, who got it from who knows where.
Dell refused to assist me with that computer and my nephew was out his money.
As for the KMS Connection Broker - doing a search online only shows me that most people don't know what it is for sure. Only one post I saw definitively states it was the Microsoft Key Management Service.
-Wolf sends