On certain older DOP-B models with early firmware (pre-2016), it was possible to downgrade to a version that had a known bug: entering system menu with a specific key sequence (e.g., pressing the four corners of the screen in a specific order) bypassed the password. Delta patched this years ago, but if your HMI has never been updated, you might try searching for the specific sequence for your model (not publicly documented for security reasons).
In DOPSoft, ensure "Enable Upload" is checked so you can retrieve the program later if the original PC is lost. unlock delta hmi password
(The most common default for high security levels). On certain older DOP-B models with early firmware
Hold the system button while powering on the unit to enter the boot menu. unlock delta hmi password