User access rights

On the WD Mirror I have change the Admin account to another name, let’s say ABCD. There are no other users configured,
I have modified the Access rights of the Default Public folder to Read/Write.

In WIn10 the WD Mirror is mapped to a drive letter (W). The WIn10 doesn’t use a Microsoft account and there are no additional users configured. So if I point Win 10 to the WD Mirror (W) and look at the security properties then only the user “everyone” is mentioned. All the WIN10 access rights are not available for the W drive. (all is blank)

Now I have a program that uses small configuration files (of media files, such as MP3) which contains peak levels, waveforms etc… The program wants to store these files at the original location of the MP3 file. However then I get errors saying that the user is not permitted access to save such files.
I tried to modify in Win10 the Security settings for user "everyone"on the W drive, but that is not allowed either, I guess since the MyCloud Mirrror uses its own security settings.

How can I solve this??