As someone else mentioned, there’s plenty on YouTube to help re form. That said, I’m helping my elementary aged kids improve their middle distance running (I’m no sprinter, so I can’t help there) and the two basic tips I’ve been using to help them:

- practice barefoot occasionally, and pay attention to how your form changes. You’re more likely to just naturally land on your forefoot when you’ve no shoes on. Now try and maintain that when you put shoes on.

- move your legs faster. Seems simple and obvious, but most people when they try to run faster don’t actually move their legs faster. They extend their stride (more likely to increase heel strike) and try to drive more acceleration off each push. You’re training for power, not speed. Focus on a higher cadence, which will probably mean you need to make a conscious effort to take what feel like _smaller_ steps.