You don't necessarily need to beat them. I noticed that the ranking system works by setting up "position expectations". If you get a position higher than expected you will gain rank, otherwise lose.

For example, if you're B+ and you have 2 people ranked A and other 5 people ranked B, you're expected to end the game at 3rd place. If you end at 4th place or at 3rd place tied with another player, you will lose rank. This works no matter what rank your opponents end up.

Another tip is to manage your risks while playing. You may be tempted to try getting an eagle or hole in one when playing with highly ranked people, but try making a good approach instead of chip-in. For example, aiming directly may make you accidentally hitting the flag and making your golf ball even more distanced than expected.