Step 1.
You need to enable "VSync" in the Game.
How do I do that?
While you're in game you need to press the "Escape" button on your keyboard.
Then press on "Options".
Then press on "Video".
Then press on "Advanced Video".
And then enable "VSync".
Step 2.
You need to get your game to run at 60 *FPS* or lower because a higher frame rate would cause some problems with getting the Achievement.
If you have a 144hz Monitor or higher, then you need to set your monitors refresh rate to 60hz to accomplish the 60 *FPS* in game.
How do I do that?

Here is a video on how to change your monitors refresh rate:
After you have done everything, restart the game.

Step 1.
Getting the right lobby level.
How do I do that?
Press on "Play".
Press on "Online".
Press on "Host".
Select the Lobby Level "Christmas".
Step 2.
You need to set your lobby to a public lobby, otherwise it will caus some problems with getting the Achievement.
How do I do that?
Again, press the "Escape" button on your keyboard.
Press on "Settings".
Go on "Invite Only" and make sure it shows "Disabled".

Now, after all of these setting changes you should be able get the Achievement with doing the following:

If you need help with this, try to contact me on my Steam Account for help.

Otherwise, if you were able to get the Achievement, I'm glad I could help!

Words marked with two * will be explained here.
FPS = Frames Per Second, meaning how many Frames Per Second your game will display.