Completely Wipe SSD on 2017 MBP

I really need to completely wipe my SSD on my 2017 MBP running High Sierra 10.13.6. I recently submitted my laptop for a warrantied repair to an Apple Repair Center, and upon receiving it back, there was a whole new set of "default" software installed on the machine - software that allowed remote access and control from a former employer (whom I purchased the laptop from through an Employee Purchase Program). These programs are embedded into the Recovery Partition, so that each time I try to reinstall a clean copy of the OS, those programs are also installed, and there's no workaround so far. I have already d/l'd and installed the Installer for High Sierra onto a flash drive; I have also created a Windows Boot Camp installer on a separate flash drive. Unfortunately, I have not found a set of clear instructions for completely wiping the SSD, including the recovery partition, to completely start anew and remove those 4 spyware/control ware programs (FileWave, Google Drive File Stream, ConnectWiseControl, and Google Keystone). Those 4 programs are doing some serious spying on a computer that the former employer has no business or right to monitor, and this seems to be the only way to get them off my system. Why Apple felt authorized to install this software onto a laptop that didn't originally have it on there is beyond me, but I am trying to take that part of this situation up with them (so far to no avail, but besides the main point).

I do not need to be warned of the caveats of removing everything from the single 250GB SSD on my 2017 MBP - I simply need to know how to erase everything on the entire drive and start with a completely new setup. For more advanced users, if there's another workaround to this (removing the 4 programs mentioned above) without completely wiping everything out, I'd really like to know what it is. Otherwise, could someone please let me know how to proceed with creating a pristine, totally clean (and authorized) SSD so I can eliminate this nightmare and move on with life?

I do have another MacBook that is operational and does not have this malicious software on it since the former employer never had access to it, so if there are some things I need to do with another Mac to perform the complete wipe on the MBP, so be it. And for the record, I will need walked through the entire process like I'm 5 years old, just to ensure I don't completely brick the newer (and significantly more expensive) laptop...

Thanks in Advance!