Is there a way to enable USB debugging from fastboot?

I have a Nvidia Shield Tablet that froze on me. After powering down it hangs on the nvidia boot up screen when I try to boot it up. Nvidia support says it is a ‘soft-brick’, as I can’t get into recovery mode from fastboot. I am trying to get a recovery image on the tablet. However, the bootloader is locked and I’m pretty sure USB debugging was not enabled ahead of time. Therefore, I can’t perform an unlock using adb, and so can’t flash a recovery image. When trying to access through a platform-tools terminal, it doesn’t show in a list of adb devices.

I’m pretty confident I have the correct drivers installed on my windows PC, which is connected to the tablet via USB.

Nvidia Shield Tablet Wifi (2014 version)

Any help is appreciated at this point, I can’t think of anything else to try. Sorry in advance for mixing up terms etc. I’ve just been researching the past few nights and trying to find a solution. I’m far from an expert.

I’ve tried these links, here and here but they seem to require USB debugging enabled or ability to access recovery mode from fastboot.