I had the same issue at first when I started playing Avorion, and it's an easy fix.
1. First, navigate to the game's install folder by right-clicking the game in Steam, clicking on the "Local Files" tab, and then clicking "Browse Local Files".
2. Inside the "bin" folder, you'll find the game's executable, "Avorion.exe". Right-click that, and there should be an option labeled "Run with graphics processor". Hover over it and click on "Change default graphics processor..." in the sub-menu that pops up. This will bring up the NVIDIA Control Panel.
3. Click the "Add" button next to the first drop-ddown menu, click on "Avorion.exe" in the new menu that pops up, and then click "Add Selected Program" to add Avorion to NVIDIA's list of recognized applications. If you ran it recently, it will be near the top of the list. Otherwise, you may want to use the drop-down menu at the top to change to A-Z sorting.
4. NVIDIA will have already selected Avorion for you in the first drop-down menu, so click on the second drop-down menu, and select "High-performance NVIDIA processor".
5. Click "Apply" in the bottom right to confirm the changes, and close the window.
Now, whenever you run Avorion, it will use your NVIDIA card by default, rather than using your integrated graphics.