https://account.churchofjesuschrist.org/help
Most common questions and problems can be solved by following the information on that page.
If you have a question or problem not answered, click on the "I didn't find an answer to my question." link at the bottom of the page and then select "Additional Support Options". You will see a form to enter information to allow the official Church Account support personnel to help you.
Church Account was formerly named LDS Account.
You may also find some helpful information in these posts:
- Updating LDS Account Information
- LDS Account Membership Record Numbers
- LDS Account Password Policies (for Church employees, missionaries, volunteers, etc.)
[Moderator edit 2/16/2020: Fixed first hyperlink, which was getting 404 Not Found errors.]