How do I put screenshot icon back on home page of iPad?

A screenshot is triggered using the iPad's physical buttons:

Take a screenshot on your iPad - Apple Support

In addition to using physical buttons, you can trigger a Screenshot with your finger using a corner-swipe gesture:

iPadOS 16 and earlier

Settings > General > Gestures > 

• Allow Finger Swipe From Corner - set to ON
• Left Corner Swipe > select Screenshot or Quick Note as required
• Right Corner Swipe > select Screenshot or Quick Note as required

iPadOS 17

Settings > Multitasking & Gestures >

• Swipe Finger from Corner - set to ON
• Bottom Left Corner > select Screenshot or Quick Note as required
• Bottom Right Corner > select Screenshot or Quick Note as required

I am guessing you mean the camera app.

First, go to the app library by swiping to the last page and then swiping from the right to the left. Look for the camera app, then hold it down and click "Add to home screen."