Step 1) Create match without bots and setup in mutator 3 goals to win....
Step 2) Open Cheat Engine and open Rocket league
Step 3) Score a goal and put you score(XP) to the Cheat Engine and click on "First Scan"
Step 4) Score second goal.
Step 5) Put the new score(XP) in Cheat Engine and click on "Next Scan"
Step 6) Take the results (+ - 7 results).
Step 7) Put a ball in front of gate ( !!! You MUST rly close the GATE YOU MUST GET A "CENTER BALL")
Step 8) Score the last goal and FAST go to the Cheat engine and RE-write the values of XP for your problem put "-10000000" this will you get + - 15 lvl from 75...
Sorry for bad english, i can make a video if you dont understand of this explain... This can be hard for u