Not a woman, but I have some advice:
Try a version of reverse chaining.
Assume that when you talk to a girl, it will go okay, she'll reject you, you'll take it as well you can, hold it together, say goodbye, and leave.
Now, your goal is just saying goodbye and leaving. That's it. All the rest we won't worry about getting right now. Greeting, talk, rejection, and shrugging it off might not go well. It doesn't matter. All you need to do is pleasantly say goodbye and leave at the end.
Once you're good at that, focus on shrugging off the rejection as smoothly as possible. Remember, a lot of these girls will have bfs so rejection might be quick.
Once you're good at that, focus on making the rejection easier for her. Never reject yourself for her, but if she's struggling, focus on being relaxed and casual so she doesn't feel like she's crushing your spirit.
Now that you're relaxed, casual, and know how to shrug off the rejection, work on talking to her a smoothly and for as long as possible before getting rejected, while still clearly communicating your interest. Get good at just talking to women before they reject you. Once you've mastered that, move on to approaching and greeting women everywhere. You don't greet every woman, but any woman. Greet them everywhere and work from there.
Chances are, you won't get halfway through this process before you accidentally don't get rejected. Practice works. Reverse chaining works. Talking works.