Important Note: Before doing this, it is highly recommend to take a backup of the database, as Data Checker is a very powerful tool.
Install DataChecker onto a machine with Access Dimensions. The install files can be found in the Dimensions install files.
Log into the affected database on DataChecker using the SA user. Use the same credentials as for Dimensions.
On the top menu, click Upgrade data for ACCESS ACCOUNTS, Generate Users from Accounts Data. A message will appear.
Read the message carefully and even take a screenshot to show all affected users. Their password will then temporarily change to the first 10 letters of their name. For example, user John Smith's password will be 'JohnSmith', and user Samantha Johnson will have their password changed to 'SamanthaJo'.
Send out a message to all affected users to log onto the database and change their password to whatever they like.