erah1612,
Thanks for those additional details. It’s expected for the icon to remain on your display, even when watching movies in third-party apps. However, if it’s stuck in the middle of the screen and you’re unable to drag it to a new location, I have some ideas that may help.
First, try toggling AssistiveTouch off, then on again in Settings > Accessibility > Touch > AssistiveTouch. Also, if you have a screen protector, I recommend removing it, restarting your iPhone, then checking for the issue again.
If the issue persists, try resetting all of your device settings back to the factory state. Keep in mind this will revert all settings that you've customized or changed (including things like your wallpaper and alarms). This means you may need to reconfigure some of those settings including network settings (so be sure you have your Wi-Fi password handy).
Before completing this step, back up your device. You can learn more about backing up your data and settings here: About backups for iOS devices. When you’re ready go to Settings > General > Reset and choose "Reset All Settings."
Take care.