You cannot recover the existing password, but you can erase it so the next time you login you will be prompted to create a new password.
Retrieve the users.txt file from your calendarscript directory.
Open in a text editor, and find the line for Administrator - probably the first line.
Find the encrypted password and erase it.
Be careful not to erase the tab characters on each side of the password.
Save the file and upload it to your web site, over-writing the existing users.txt file.
If necessary, CHMOD 777 it to make it writeable.
The next time you login as Administrator, use any password and you will be prompted to change your password after logging in.
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Scott
CalendarScript.com