To stop Microsoft Teams from launching on computer startup you need to first start Task Manager. This can be done by either pressing ALT+CTRL+DEL and then selecting Task Manager, or by right clicking on the task bar and selecting Task Manager.
Once Task Manager starts up you will see the window below, click on <More details> located in the lower left hand corner.
Next select the Startup tab across the top to view what items "Startup" on logon.
Locate and right click on Microsoft Teams from the list and then select <Disable>. You can alternatively select Microsoft Teams from the list and then click on the <Disable> button from the lower right corner.
Microsoft Teams will not longer start on computer startup. NOTE: This procedure needs to be followed each time a new user logs into a new computer that they have not used before.