You can start training by just riding more, longer and faster..... as your body allows. In time, you will get stronger, have better endurance and technique.
Remember one thing, it never gets easier, you just ride faster. Use an app like "Strava" to track your rides and motivate you to push yourself to limits you haven't realized yet.
If you have true desire and want this, it will happen over time, not overnight. Good luck.