How do you unlock iceberg ruins on Pokemon pearl?

You can't unlock the Iceberg Ruins in Pokemon Pearl. The Iceberg Ruins are actually a location in Pokemon Diamond, not Pokemon Pearl.

There's a good chance you're thinking about the Snowpoint Temple, which is located in Snowpoint City in Pokemon Pearl. To reach it, you need to:

1. Defeat the Gym Leader Candice in Snowpoint City to get the Ice Badge.

2. Defeat the Galactic Commander Saturn in the nearby Valley Windworks.

Once you've done these two things, you can enter the Snowpoint Temple. It's filled with ice-type trainers, but there's no specific "unlocking" process.