With access to the database
mysql -e 'update itop.priv_user_local set password_hash="$2y$10$vRSLaXl12M7Y70Ucf6KbLuzb.tZbeypqKyZHXWkjgeJCrPYfFwv9a" where id = 1;'
will set the password to admin
(for the account with id=1, should be admin).
Keep that in your shell history, because MySQL history ignores any command with password
in it.
With access to the itop install files
With the iTop toolkit installed.
There is a reset_admin_account.php
that you can download here and put in itop/toolkit
folder, the password admin
is too simple and not accepted, you must edit it to have something more secure, then just go to the page.