You might want to practice a lot.
I have a friend who had trouble saying anything beyond a word or two a lot of the time, and she got a radio and a tape recorder, and practiced saying things that people on the radio said.
The change didn't happen overnight though. She first got good at making speeches, because those were memorized, and after several years she was able to use sentences in everyday conversation.
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"In my world it's a place of patterns and feel. In my world it's a haven for what is real. It's my world, nobody can steal it, but people like me, we live in the shadows." -Donna Williams