In the internet I found a sollution of the problem:
The password of the component is stored in the following a php file on the webserver
"/components/com_expose/expose/manager/amfphp/extra/passhash.inc.php"
There I should replace the only line with the following one:
<?php $GLOBALS["passhash"] = "3e892e9edc898cf713ecd6ef06a116a7"; ?>
After this step the password is reseted to 'manager'.