First thing to check: are you using the right version?  We recently released a new version of GetItDone.  There were significant changes that required version 5 to be a separate app (read more).  As a result, there are 2 versions of the app in the app store and online.  

Here are the links for the new Get It Done 5:

And here are the links to the old Get It Done Classic :

If you are using the right version, then you can reset the password from the login window.  Here's what it looks like on Get It Done 5: