That's the thing: you can use basically whichever pronunciation or grammar you want. Since it's already non-standard language, prescribing how to use it is beyond pointless. But if you absolutely need prescriptions, then my own tendency is to use the paradigm ꙮ/ꙮm/ꙮr/ꙮrs/ꙮself with singular agreement, and the readings I use are seraph/seraphim/seraphir/seraphirs/seraphimself, sometimes indicated with ruby characters. But again, you're under no obligation to use even remotely the same inflections or readings — that's part of the fun.

As for the background:

The character is the Cyrillic multiocular O, which appeared exactly once in exactly one 15th century Old Church Slavonic manuscript to write the phrase "many-eyed seraphim". That is, ⟨ꙮ⟩ was originally a fanciful variant of the Cyrillic O, meant to look like a bunch of creepy eyes. After the letter was encoded into Unicode, it became a somewhat popular symbol online, often used for a sort of comedic horror effect, for instance by writing "ꙮwꙮ" instead of "OwO". This would've been at the peak of the whole "biblically accurate angel" craze.

It was from this horror-comedic usage of ⟨ꙮ⟩ that my closeted self first started replacing my deadname with ⟨ꙮ⟩ in certain contexts, under the pretense that I was "just being silly" and that "these people don't really need to know my real name, do they?". Later on, I saw that a few other people were using ⟨ꙮ⟩ as a neopronoun, so I decided to start experimenting with using that character as a neopronoun, too. I think that an essentially unpronounceable image of a bunch of eyes really captures the whole "wrong planet" vibe, and these sorts of Unicode/emoji neopronouns in general are a really creative use of language, since they're basically a form of mixed-script writing.