How to pair the Apple Pencil (1st generation) with iPad Pro?

You don't.

You purchased the wrong version of the Apple Pencil.

2018 and 2020 iPad Pro model iPad Pros use the newer, 2nd generation Apple Pencil.

If you just purchased this 1st gen Apple Pencil, return it from where you purchased, get your money back and purchase the 2nd gen Apple Pencil, instead.

Sorry, Best of Luck to You!

You don't

Apple Pencil compatibility

Find out which Apple Pencil works with which iPad.

Apple Pencil (2nd generation)

You can use Apple Pencil (2nd generation) with these iPad models: 

• iPad Pro 12.9-inch (3rd generation) and later
• iPad Pro 11-inch (1st generation) and later

Apple Pencil (1st generation)

You can use Apple Pencil (1st generation) with these iPad models:

• iPad Pro 12.9-inch (1st or 2nd generation)
• iPad Pro 10.5-inch
• iPad Pro 9.7-inch
• iPad Air (3rd generation)
• iPad (7th generation)
• iPad (6th generation)
• iPad mini (5th generation)