Currently iTunes, Spotify, and VEVO pull their biography information exclusively from AllMusic. They have an editorial team that takes information provided to them and creates biographies that are then used by these partners on the associated artist pages. There is no guarantee that your submission to them will be used by their editorial team for the production of editorial content. Per AllMusic priority is determined by "current popularity, historical or artistic importance, and the needs of our data licensees.”
Submissions can be sent by email here using the music submission email. Alternatively a physical mail submission can be sent to the address provided.