Who granted immortality to 🧝Earendil?

[TheManInTheMoon]

So in Silmarillion the phrasing makes it look like Manwë granted immortality to E couple.

But in Tolkien letters: "Immortality and Mortality being the special gifts of God to the Eruhini (in whose conception and creation the Valar had no part at all) it must be assumed that no alteration of their fundamental kind could be effected by the Valar even in one case: the cases of Lúthien (and Túor) and the position of their descendants was a direct act of God."

So what does that mean? Did Manwë grant E couple and their kids immortality and mortality through Eru? Or did he do it without praying to Eru?

 

[Melkor]

I think that Manwë did it through Eru (as in other cases). But this is just an assumption, maybe someone provide source which bring light in to this matter.