Try practicing in low-stakes situation. Make an effort to make small talk with the cashier at the store. Maybe have a short chat with the person in line behind you if they seem open to it (use your introvert radar, we are usually pretty good at reading non verbal cues from someone that wants to be left alone). Make sure to pick neutral, inoffensive topics (Weather, yes. Politics, no) and aim for short interactions.

The idea here is to get in some practice in an environment where there is minimal chance for negative consequences. If the interaction ends up being awkward, its easy to stop. Worst case scenario a stranger thinks you're a bit weird and then goes about their day, never having to see you again.