You should be able to play this song in less than a week, if you can't, please play songs from level 2
The best way to learn this song, or any other song, is to watch the video at least 10 times, if it is necessary, please watch the video more times, until you feel that you understand the song, and you are familiar with the tune. Concentrate on the movement of the keys on the piano first and then look at the actual notes on the staff, feel the music and try to sing along with it. Once you start to play the song, feel free to come back to watch the video more times.
Once you are familiar with the song, and how it sounds, then print the music score PDF below.
Now, with the actual music sheet on your hands, play the video a few more times and put your eyes on the paper, and read along with the music, listen to the song while looking at the music sheet. Now that you have two hands, it's very important to understand how to study better.
Count the measures in the song, the same as you did it in level 1 and level 2. All songs in level 3, now they have two hands. The right hand plays the melody, and the left hand plays the accompaniment, sometimes is two notes of the chord, or one, or it can be the full chord.
FIRST: PLAY THE LEFT HAND (CHORDS). Read the notes on the left hand. If you can not read the bass clef good enough, watch the video so you can see where you have to play the notes.
SECOND: PLAY THE RIGHT HAND (MELODY). Then play the melody with the right hand. Because you are playing songs from this level, it means you already can play simple melodies, with the right hand by it self. So playing the melody should be easy.
THIRD: Start playing two hands at the same time. Each day you have to learn so many measures, or a part of the song. DON'T LOOK AT THE WHOLE SONG, IT WILL BE TOO MUCH.
Play only 2 or 3 measures or any part of the song for that day, think of it, as the complete song. Play it over and over and practice until you can play those few measures. If you get tire of practicing, take a break, and then come back to keep doing it.
Once you can play those measures without mistakes at least 5 to 10 times. Then relax, and the next day do the same, with the next few measures. If you practice like that steady and constantly everyday, you will learn to play the song, and you will be able to play the piano much better