You might get this trophy naturally through play but, if not, it’s easy to engineer.
Set up a 2v2 exhibition with no bots and use a second controller. Set goal limit to 2. Save the goal first by the second controller hitting the ball into you on your goal line.
Switch teams so you’re both on the same side. Score a goal with nobody there to stop you.
The assist is only slightly more difficult as you need to have hit the ball right before your teammate does for it to count. You can park the other car next to the goal line and hit the ball into them so it goes in after. Will count as assist and will come up saying so, along with your trophy.