Hi,
It's been some time since I first noticed Quenya didn't include a gloss for "to forget" among its vocabulary, so that I came up with another option and would like whether is it valid or not for personal use. Ollum-, primitive verb.
Explanation; basically rendering lum- as a verb having to do with time and the adding the or- preffix to denote surpassing or excessment, which I once saw used on this site for such meaning in ortimno "guardian". Much like the distinction between the bare verb "run" and the compound "outrun" in English. Something like "(to be) overtimed/outrun by time" might be taken from this expression as the form ollumina.
I don't really think this to be the best option out there though. Perhaps an expression like "My heart no longer keeps it" or "My mind has left it" could better fit the purpose for this gloss. Perhaps Tolkien himself intentionously obviated an strict word for "to forget" in favour of a fancier dict for us to discover decades after him. Edit: I already knew from laisa-, my bad.
And lastly, this might have been previously said here, but Christopher Tolkien passed away on 15th January and left most of us with an extraordinary legacy of his father's work, which we all should be thankful for. May he find rest and peace in Mandos, or perhaps, beyond our known world. R.I.P. Christopher Tolkien.