Here are the complete and correct steps:

1. Enter preferences:

On the contract trading page, click "⋯" (more options) in the upper right corner.

• Select Preferences.

2. Switch position mode:

• Find Position Mode in Preferences.

• Select Two-way position mode and click Confirm.

3. Start trading:

• Return to the trading page and place an order normally to open long and short orders at the same time: