First, you'd need to buy something to play back the tapes. If you still have the camcorder they were recorded on (and if it's still working) that would be perfect. If not, you'll need to pick one up used from eBay or something. It's possible to get stand alone Hi-8 players, but they're normally much more expensive and not really any better for your use case.

Every camcorder should have a video out port, but there are lots of different models out there so check that it has one before you buy. From what I've seen, Hi-8 camcorders normally have 3.5mm AV out ports. That means you'll need a cable like this.

Whichever port yours has, you'll need a capture card compatible with it. You can get capture cards pretty cheaply on Ali express. I've never used it personally, but this one has some pretty favorable reviews.

So, at this point you have your camcorder, your 3.5mm av out cable, and you're capture card. You also need a computer with OBS installed. What you do is plug the av cable into your camcorder, plug the av cable into the capture card, and then plug the capture card into the computer. I don't often use OBS (I'm using it in this guide because it's free), so I can't remember exactly how to set it up. But what you need to do is select the capture card as an external capture device, and then tell OBS to record from that device. I don't think I will be hard to work out with a bit of internet searching.

Once you have all of that set up, all you need to do is tell your camcorder to play the tapes! It should automatically playback through the AV out, and you'll be able to watch the tapes through OBS as they're being recorded.

Hopefully this isn't too complicated or expensive. Once you're done, you could try to re-sell your camcorder if you want to recoup some of the costs. Good luck!