Simply 'click & drag' on a blank space on the bar, pulling it back to where you want it to be. Don't worry when it doesn't work first time; it rarely does! Just keep trying; it will work eventually.
When you've got it back to the right place, right-click on it and select 'Lock Taskbar' to stop it moving again.
Right click on the taskbar and untick the Lock the taskbar menu option; then left click and drag the taskbar back to the bottom of the screen; and finally make sure the Lock option is ticked to keep it in place.