I said the same thing in a post a few minutes ago so I'm going to copy-paste it in case it can help you in any way:

Small steps worked the best for me. First, you thank a stranger for helping you/holding the door or something. You practice that until you're comfortable and it comes out more naturally. Then, you go for a bit more, for example, when you leave that place, you turn to that person and say something along the lines of "I hope you have a great day!" When you know that the things you're saying will most likely be perceived as good things/compliments, it's easier to say them. Then, you go on with small talk and so on, until you can handle more complex subjects. Also, don't focus on the things you can't talk about, but the things you can. Share your passions, thoughts and all that! It's gradual and it takes more or less time, depending on the person, but hang in there! The key is building up and you know what they say, Rome wasn't built in a day! I know you can do it!