1. The first problem is the fast notes in the right hand. You can play them more slowly. Or leave out some notes: watch the video.

The left hand is using the notes of the chords. About chords: https://youtu.be/7U0DfLRxSBU

Each (basic) chord has a fifth note and a note between. Check HowToStart7
G minor: G-Bb-D
A major: A-C#-E
D minor: D-F-A

In this piece those chord notes are spread over the "left hand area". If you understand these chord notes, you will find it easier to play the same notes spread out on the left hand.
I would play them like this:

Here is the first part slowly:

2. Start practicing the right hand solo. You can even start with the 'less notes part', as I do in the Autumn, Autumn, Autumn, Lachini, 1 .

Then play together with the left hand, with the 'basic chords', as in the video "Autumn, Autumn, Autumn, Lachini, 2 ". Focus on those three chord notes of each chord!

Those chords can be played in another way, (that's the 'secret' of playing the piano!) On this sheet you see some explanation. I use the octave + fifth (last one on the sheet) to play the chords in an easy way. First try that:

In the video at 0:30 you can see what happens with the D minor chord. It is spread all over the keyboard - like a painter who spreads the paint all over his canvas.

You use both hands. It's a good exercise to do with several chords.
If somehow you need to use other fingers (every hand is built in another shape, so you have to feel what fits best) you have to figure out what's best for you.
It is important though not to change the fingering you chose at last. Your fingers need to get used to one pattern.

3. The chord notes are spread all over the keyboard, but mixed up (the names are notated in your sheet too, you can check them there if you want):

How to study? You can play the chords simplified:
•less notes and more simple patterns, or
•memorize them as they are, or
•use the sheet and read the patterns, the patterns on this sheet can help, and the knowledge that all the notes in these patterns are part of the chord makes it a bit easier too.
(You even can notice that the main notes of the right hand, the melody, fit in that chord too...)

Here I explain why chords are mixed up:

4. The right hand notes (the melody) don't always 'fit' into the chords.
Music that sounds weird, or complicated, or odd, (some people like it, others don't) is kind of 'messing' with those rules.
That's what artists like to do; engineers better not ;)

Also the chords will often have some other notes added. I call them the 'spices', to add some flavor.
In this video I show a nice phenomenon about melody and chords. A reason that music can be so wonderful:

5. This video is part 1, after the intro, the first two minutes of the original file, in slow motion.

This video is part 2 in slow motion.

This video is part 3 in slow motion.

This video is part 4 in slow motion.

6. As I explained (STEP 3), the pianist mixes up the chords. It would be easier if he used the same pattern for each one. Still you do find some patterns.
The colours here show a repeating pattern.
It would help to play them with the same fingers each time: the red one as 5 2 1 2 and the green one as 4 2 1 for example. (I didn't play measure 2 this way on the video, I know)

About the chord notes without a colour, you can decide to play them at random, if you so choose. For example measure 9: f a d f a d can be f d a f a d or watever...
Really, there will be almost no difference. I am quite sure that the master will do that too: those musicians often play such 'details' one week otherwise than they did the week before.