Top menu bar > Settings > Options > all the way to the left = Setup.  Go down to "Default Letter Folder".  1 should be the master/generic/default letter from Lacerte.

Bonus info 🙂

To create custom letters - Settings > Client letter.  You can create your own customized letters from there.  Be SURE to start a new one tho, don't edit the default one (or you'll regret it... been there, done that...)