You need to complete several park goals in Tony Hawk Pro Skater 1+2 to advance through the game. Many of these challenges test your skills to steadily increase your ability to earn a higher score, combine various moves, and find collectibles in the course. Some of the park goals also require you to perform moves at specific locations on the map. On the Warehouse level, you need to do an ollie over the channel gap.
The channel gap is the three half-pipes on the side of the wall that you enter the level. Make it down the ramp and go to the left. The best way to complete the challenge is to jump onto the small platform on the right side of the room. Angle your skater on the side as close to the wall you can get them. When you’re ready, have them ride straight out and jump right before they hit the side. They should clear the gap and make it to the other side, or go down the side.
As long as they make it to the other side without falling, it should count for you. You have a few different methods to complete this challenge, such as launching off one pipe doing an ollie and landing on the other ramp. Both ways are valid and work to achieve this goal.