To hide your search box, press and hold (or right-click) the taskbar and select Search > Hidden.
If your search bar is hidden and you want it to show on the taskbar, press and hold (or right-click) the taskbar and select Search > Show search box.
If the above doesn't work, try opening taskbar settings. Select Start > Settings > Personalization > Taskbar. If you have the Use small taskbar buttons toggle set to On, you will need to turn this Off to see the search box. Also, make sure the Taskbar location on screen is set to Bottom.