To close a partial portion of a trade in MT5, follow these steps:

1. Locate the trade you want to partially close in the "Trade" tab of the "Terminal" window at the bottom of the screen.

2. Double-click on the running trade.

3. In the "Order" window, you will see the current parameters of the trade.

4. Adjust the "Volume" field to the desired amount you want to close. For example, if you initially traded 1 lot and want to close half of it, you can change the volume to 0.5 lots.

5. Click on the "Close" button to execute the partial closure of the trade.

6. You will receive a confirmation message indicating that the partial closure has been successful.

7. Monitor the remaining portion of the trade in the "Trade" tab of the "Terminal" window.

Note: Partially closing a trade reduces the position size while keeping the remaining portion open. Make sure to carefully consider the size and impact of the partial closure on your overall trading strategy and risk management.