How can I setup reverse DNS for my reserverd IP?

I need to define the rDNS for some RESERVERD PUBLIC IP's provided by Oracle on my tenancy. There is no option to define it on panel.

I already readed some docs, but, they apply olny for private or self owned IP's.

I think I must have misunderstood something, and I apologize in advance for that.

Thanks for help, anyways.