Sandstorm is a great TM for your Pokémon to learn since it lasts for multiple turns. This move causes a sandstorm to wreak havoc on the battlefield for five turns. Any Pokémon that is not a rock or ground type gets damaged each turn that the sandstorm is raging. To find this TM in Pokémon Brilliant Diamond and Shining Pearl, you’ll need to do a few specific things.
Before you can find this TM, you will first need to defeat the Elite Four and become the champion. After you have done this, you can head over to Snowpoint City and talk to the sailor to get a ride over to the Fight Area. Now that you have completed this step, it is time to finish your Pokédex. To do this, you will need to see every Pokémon in the Sinnoh region (there are 150).
After you have accomplished both of the tasks above, you will be allowed to head north of the Fight Area to Route 225. Follow the route until you reach Route 228. You will know when you reach the correct area when you are caught in the middle of a sandstorm. Follow the path south along the left edge and you will come across an elite trainer. Defeat them and continue south until you come across the pair of Pokémon Rangers. Next to the Pokémon Rangers, you will see the TM.