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Launch Skype for Business.

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Click the gear icon (⚙) in the top-right corner

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In the Options window, select Personal from the left-hand menu.

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Under the My account section, uncheck:
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Click OK to save your changes, then close Skype for Business.
Option 2: Disable via Windows Startup Apps
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Click the Windows Start menu and type Startup Apps in the search bar and Select the one showing as in screen shot below.

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Find Skype for Business in the list of apps and toggle the switch to Off.
