cannot get rid of floating white circle that launches emergency SOS

When I first tapped a test stating "assistive technology", a floating white circle on gray background appeared, launching a siren, then 3-2-1, and direct call, apparently, to emergency services. I rebooted, then turned off the suggested emergency buttons in Settings. Now, the floating white button reappears, without sound, but opens a screen showing "Power off, Emergency SOS, and x Cancel." How can I get rid of this white circle?