How to release email-adresses

Dear Cloudflare community,

I’m not quite as versed in this topic as I’d like to be, so please pardon my naive question.

I’ve recently signed up for a certain domain “XYZ . com” at Cloudflare via the iPhone iCloud+ settings menu, which was quite easy.

I was able to register my own Mailadresse, let’s call it “a@XYZ . com” and all messages are forwarded correctly.

I’m also sharing my iCloud+ subscription with my partner and I wanted to grant her her very own mailadress on my domain, let’s call it “b@XYZ . com”.

However, I didn’t know that I had to set up her adress on her device first and instead set it up on my iphone.

After noticing my mistake I deleted “b@XYZ . com” from my device and tried to add it to hers instead.

But now I get the message that the adress is already in use.

So my question is:

How can I release the mailadresse “b@XYZ . com” after adding it to the wrong device?

Thanks in advance and best regards