I have a couple of ideas, im not sure if any of them will work but if you haven't tried them already, maybe give them a go?
1. Try and make it more fun, if you play games to revise the content then might find it a bit easier
2. Build up your revision time, yes GCSEs are very close and its terrifying, but you'll never get anywhere if you try and do loads straight away so maybe start at as little as 20 minutes a day and build up every day
3. go somewhere where you're forced to revise, like if you have a local library where lots of people study, you cant really do anything but study
4. Try and reduce everything you want to do into just 5 minutes, for example if you want to make notes on a topic tell yourself you'll do it for just 5 minutes and it'll seem like a lot less effort and less overwhelming, and there chances are you'll carry on for just a bit longer anyway
5. Try the pomodoro technique where you work for 25 minutes then have a 5 minute break to stay focused, of course you can adjust the length of time for breaks or studying to suit you
6. Make a detailed plan, most people are significantly more likely to do something if they've written it down, maybe even tell you friends or family so they can hold you accountable if you don't do it
7. Figure out the reason why you cant seem to do any revision, whether its fear of failure, perfectionism, burnout, your mental health problems and try and find a solution for it
8. Do a detox, don't touch a screen for a whole day, or even s couple of days if that what it takes, until revision becomes the most interesting thing you have to do. Before then, maybe read some books or go on walks
Hope something helps?