Question

How do you dig up items?(underground)(diamond)?

Comments

you stick a shovel/picaxe/any digging material into the ground and you move the digging material down and up and In the process you must be digging up dirt. Eventually you will find special items from the 1800s.

Answer 1

Do you mean Mining?
>To mine, the player must find a spot where the wall 'pings' by touching the screen and looking for sparkles. These spots will appear randomly in the Underground, usually in clusters, and can be located by looking for sparkles marked on the radar screen.
The player digs into the wall with a pick, which chips away small areas of rock, and a hammer, which breaks a larger area of the rock. Each spot will hide one to four items, including spheres, Fossils, Revives, Heart Scales, shards, evolutionary stones, Plates, and a few held items. -Bulbapedia

Anyway basically you need a pick and look for sparkly areas, and that's where you'll find items.

Comments

Shoot! Just a couple of minutes after you!!! ...Oh well

Answer 2

You have to get the Explorer Kit from the man in Eterna City. Next to Pokemon Center.
Once you get the Kit and you used it to go underground, tap on the screen in several spots. Watch for the shiny diamond stuff. Press A on those shiny spots. Then you can start digging. Usually you'll find spheres, but you can occasionally find revives and fossils.