Listen to several renditions of "Anand Sahib" on YouTube or from a streaming audio source.
Select one that has clear, distinct sound. The best versions are easy to follow by tapping your feet to the rhythm, or by singing or humming along.
Take note how the various sections of music differ or are the same. This musical genre -- a sung prayer -- is composed of melodic formulas that have simple, regular patterns.
Draft a basic outline of the song's form. Each section is repetitive and follows a simple melodic contour, usually stepwise or skips in the interval of a third.
Using the beginning letters of the English alphabet, begin identifying sections such as A, B, and C. In the case of a section that is like an already-identified section but with slight variations, use a symbol to distinguish them, such as A', and B'.
Listen to the recording several times, until you have identified all the unique musical sections, then make a note of how many times each section is repeated.
Using the five fingers of one hand, learn each section by ear. Stop the recording and rewind as often as needed until you are comfortable with the scope and order of the notes in each section.
Play along with a recording. Remember that the harmonium does not play every sung note, but only outlines the melody. Thus, some variation between performers is possible.
After several repetitions and having gained confidence, you might wish to make your own musical notations to aid in your performance. Or, you might find that your playing is more expressive when playing by rote.