If you device dimmer Master is a single channel dimmer you need use the single channel device association, unless your manual says otherwise.
This link has how use the driver Z-Wave Device Config Mc that is the same that use with Child device config created.
On this page, in the preference “Select Z Wave Device Action” you can select the different configuration and association functions
Because the app does not show the labels of the custom capabilities well and shows the creation name of the capability
When you have finished with the association and see that it works, you must delete the child device configurator. You can create it again when you need it
The DNI of the device receiving the command can be seen in the “Device Fingerprint Info” option.
In this case it would be the DNI of the Master dimmer and the association must be done in the Accessory dimmer, which is the one that will send the on-off or level command to the Master dimmer