Trainer Needed For 1 Cat In Chicago

My 11-month-old cat has been scared of open windows and open patio doors. When he was younger, one of the windows shattered (the outer layer), therefore a lot of people came in to replace the window. The loudness of it all scared him and he now runs and hides behind a standing mirror whenever a window or the patio is opened. I'd love to help him get used to the fresh air and not be afraid of them as I frequent the balcony a lot in warmer climates.