Write to them anyway. That's the ritual, whole: letters to someone who will never read them - which sounds like the saddest thing in the world until you try it and find out what it actually is.
Thinking about them loops; writing to them lands. A letter has an address. "Dear Dad" puts you in the second person, and suddenly you're not ruminating about him, you're talking to him - the news, the thing you saw that was so him, the sentence you never got to say, the fury, the thank-you. The pen finds things thinking never gets to.
How, if you want a shape
- Start with the date, then "Dear" and their name. Ordinary letter. That's the spell
- Tell them something new. The dead miss the news; catch them up
- Say one true thing you couldn't say to a living face
- Sign it how you always signed things to them
The not-being-answered is part of what helps. An answer would make it a conversation with all a conversation's caution; the silence makes it confession, and confession travels light. In their garden here, there's a postbox for exactly this - letters fold, seal, and post into somewhere kept. Or paper, or the notes app at 2 a.m. The address was never the point. The writing is.