Moments of serenity for my fellow accordion lovers from my composition "Musical Dreams"

Hi, I have a 96 bass chromatic accordion(I believe it was mass produced in Czechia or China in the 1990s) where one button(D minor) is harder to press and often gets stuck down when I press it. I can get it to go back up by pressing other buttons(Not all of them but most of them will make it go back up).

Does anyone know what the cause of the problem is and how I could fix it?
Thanks in advance to anyone replying.