In general, we just... do. What that looks like is going to be different for everyone and how you get there will be unique to you, but even without trying you almost certainly just will... get over it. Necessity if nothing else will help with that. You've still got to feed yourself, maintain your friendships and any other relationships you have, pay your bills, advance your goals and carry on. Life doesn't typically care very much that you'd really rather just put it on hold and ruminate for a while.

I guess that doesn't sound very helpful but time has a way of doing the getting over for us. Sometimes you need more of it, depending on the source and magnitude of your pain, but eventually enough time is all you need.

To put it in perspective, if you've ever experienced this before, the previous crush likely doesn't feature too loudly on your radar right now and yet they might have been your whole world at one stage. If this is the first time you've been through this, it probably won't be your last and there are probably similarly painful experiences in your past that seemed very important to you when they were fresh that are all but forgotten now. Try to remember that you walked that passage from all consuming fixation, to just a memory before and you can walk it again.

On a more practical level it probably would help things go faster if you could avoid too much contact with the person for a while so you don't have to keep raking over the unpleasant emotions associated with the rejection and don't have to keep fighting the urge to try your luck again when reminded of how much you like them, but then again often work or school or other environments can force you to have to see someone repeatedly even after there's awkwardness between the two of you. In that scenario, well, to repeat the initially glib and unhelpful sounding advice, it'll just happen with time, even when it feels like it won't, don't worry - you will get over this.