The main reason why most people get diagnosed with insomnia is just because they find their body isn't falling asleep exactly when they want it to and they panic over it so they are even less likely to fall asleep, so first, don't ever panic. It's okay.

Try getting up and doing some exercise, getting physically tired can reduce how much you think if you're overthinking while in bed and can give you hormones to help you sleep.

Try wearing a sleep mask, a thing that will keep your eyes shut, since that can signal to your brain that it's time to sleep.

Try meditation, or relaxation exercises based on that. One of the first recommendations you get when learning to meditate is to put yourself in a posture where you won't fall asleep, like sitting down on a chair but without resting on the backrest, because it's easier to fall asleep while doing it, so you can do the opposite and encourage that instead.

Here's an exercise I do occasionally: make sure your bed is properly made, the pillow is comfy and you're not feeling weird bumps in it, the sheets are not wrinkled, etc., then lie down on the bed, ideally flat on your back with your arms alongside your torso, and tuck yourself in nicely. Close your eyes, then focus on the breath a little bit. Don't change it, just watch over it, notice how it's doing. If it's going too fast, if it's too shallow, just keep watching and wait for it to calm down. Once it's calmed down, focus on the very top of your head. If something feels tense, relax the muscles. Then keep on focusing on every body part from top to bottom, all the way down to your toes, and relax each muscle. If you get distracted while doing this, it's fine, just go back to doing that when you notice that. Once you're done, at the very least you'll be more relaxed, and maybe you'll find it easier to keep your eyes closed, and maybe soon you'll fall asleep.

Or just get up, and go do something that does not require too much thinking or provokes too much emotions (don't go reading books that make you cry or make you mad at the author for example) and avoid screens.

Or become ungovernable, choose to just not sleep, and carry on with a very long evening until you find yourself sleepy, if you're fine with having maybe a tiring day tomorrow or waking up late.