Drain any static from your body before removing the drive. There is the possibility that SR can harm a drive if it's close to failing as it works them hard.
You'll have to determine the drive interface type.
Could be PATA:
This chapter, from the 21st edition of <em>Upgrading and Repairing PCs</em>, provides a wealth of technical information about the IDE/ATA drive interface specification.
www.informit.com
Could be SATA:
This chapter, from the 21st edition of <em>Upgrading and Repairing PCs</em>, provides a wealth of technical information about the IDE/ATA drive interface specification.
www.informit.com
Or something else. You could put the drive directly into your PC if you have the right ports and connections. Or you could look for hard drive caddy, enclosure, or hdd docking station on Best Buy or Amazon. You'll also need the proper interface to your PC if it's an external enclosure. USB 2 is dog slow. USB 3 is much better if your PC supports it. But, there are threads here on the forum about whether SR can recognize a USB drive and it's not guaranteed. It might work if the BIOS recognizes the drive.
If you get a double drive docking station like this,
you may be able to back up the drive with something like Terabyte Image for Windows which
@Steve has recommended in the past. The docking station may come with software. Also, the maker of your target backup drive may provide software. Note that it's possible the Tivo would reject the copy though as everything in there is probably encrypted.
If you have a laptop and you don't mind removing the cover, and it has an optical disc player, you can replace that drive with something that holds a SATA HDD / SSD, like this:
If that link doesn't work, it's Amazon product number B01MRI8YFN.
You can also destroy your laptop that way if you're not careful.
Hope this helps.
May your bits be stable and your interfaces be fast.

Ron