Best bet is to start mewing.
I'm pretty horrified at the DIY solutions here, and even if you manage a result through mechanical means, it will disappear if you stop the "treatment".
You have to do it the way the body is meant to function: move closer to a paleo diet, chew gum on both sides, and mew.
The tongue will push the teeth apart and into the lips, which will keep them aligned.
Be reminded that significant changes can happen over a period of ten years, and it's only a fraction of your active life.