In short there is no way of resetting the password. You will have to send the control back to the service of Boschrexroth to reset the control to factory state. All data will be lost in that case!
EDIT: As an update to this thread please have a look to this topic.
We always suggest to add a backup user with full rights to the system so if one is blocked the other could be used.
As an update to this topic:
In the ctrlX CORE Runtime Release notes for RM21.11 (version 1.12) that can be found on the collaboration room or also in our online documentation is the description for image update/factory reset, that you can use.
There it's described in the chapter 2.3.1 for real cores, 2.4.1 for virtual cores but for them the easiest way is to simply create a new one in the new installed ctrlX WORKS.
Beware that from the release milestone RM21.11 (version 1.12) all application apps needs a license to be able to run.