Computer Hope

Imac Catalina Version 10.15.6 - using Microsoft blue tooth mouse.  The right click of the mouse no longer functioned - unknown reason.  So - I went to Systems Preferences / Mouse / Primary Mouse Button and changed the primary mouse button selection from left to right.  I wish to change it back but mouse functions do not work correctly.  In 'mouse', the mouse pointer is flashing in the search window.  I can not get to the 'left' button to change it back.  Suggestions?