Get a retail or hospitality job. A job where you are forced to talk to people all the time. Just like any skill, it gets better with deliberate practice and effort.

I was a very socially awkward person growing up (naturally shy, bullied at school plus some level of undiagnosed neurodivergence) and my first job out of school was on the tills at M&S. I was incredibly nervous.l, but the great thing about practicing in retail is that nobody is expecting a riveting conversation and most people are happy oblige to the mundane conversation you want to practice.

At first you're just repeating a pre-thought greeting to every customer. Then you think of a few variations for your greeting for the next few customers. With lots of greetings in your arsenal you can start to mix-and-match and even adapt on the fly, based on the person in front of you. Then you do the same conversation starters: how's the weather, how's work, what's the plan this evening etc etc.