Amazon will always default to the last account that you logged into. That doesn't matter is you logged in at the website or the Alexa app. If your last login was at Amazon.com, then click on Account for current_account_name and select, Switch Accounts (top, right, below your name).
OTOH, if you were logged on to the Alexa app last, then select, Not your_login_name (bottom of left side panel).