Write an Android application

I have a Used car website already running on wordpress. I have installed a Auction platform plug in also for the same. It is working in a way but there are certain issues with the platform which I need to work on. Issues are small but you need to have an in depth knowledge about wordpress and programming to fix it since the old developer of my website did not do it well and left things a little messed up. For eg - I have enabled users to register from the link for auction but once users try to register it says an email has been sent to your email but then there is no email received by the users from WordPress. Need to fix this bug.