Whenever I try to download a app “confirm with assistive touch” always pops up d

Hello,

I am thinking you likely accidentally enabled it with an unintentional triple-click. That will also turn it off for you.

Use AssistiveTouch on iPhone - Apple Support

"Tip: To turn AssistiveTouch on or off quickly, triple-click the side button (on an iPhone with Face ID) or triple-click the Home button (on other iPhone models)."

I hope this helps.

Have you enabled Assistive Touch? Use AssistiveTouch on your iPhone, iPad, or iPod touch

It would be better if you can please re-post with a screenshot, in order to understand the phenomenon better. Images/pictures speak louder than words. 

Please understand this is a public forum: While attaching a Screenshot, do not provide any personal credentials, such as IP address, Card detail, email id, apple id, IMEI number, Serial Number, Phone number, Order ID, if you are sharing a map ensure your location is not identifiable, etc.

Instead of Double Click to confirm App Store purchases, it is looking for Assistive touch if you have enabled it on your device.