Start by playing the three single bass notes before trying your hand at further bass chords. You will find the three single bass notes in the middle portion of your accordion. Place the middle finger of your dominant hand on the little rhinestone on the accordion. As for your index and fourth finger, they would go with the middle finger while playing the three single bass notes. With enough practice, you would eventually learn C, F and G.
Move your fingers down towards the palm of your dominant hand from the position in which your fingers originally were while playing the three single bass notes. By doing this, you would be able to find the major chords equivalent to the three single bass notes. You would want to keep in mind that three or more notes when played simultaneously make up one chord. During the manufacturing process, accordions are set up in a way that the musician can accomplish this by pushing just a single button on the accordion.
Notice that no matter in which order you play each of the single notes, the response from the accordion is the same. Once you have found the G single note, all you need to do to find the G chord is to move diagonally downwards from the G single note. The same holds true for F single note and F chord on the accordion. Spend at least a few minutes to understand the sound difference between a single note and its corresponding cord.
While playing accordion, the switch from a single note to a matching cord is called the 1-4-5 pattern. Fully understand this concept. The 1-4-5 pattern is commonly used by musicians while composing folk and rock music. It is important to fully understand the 1-4-5 pattern because usually, it is the key to most songs.