This should be obvious but I’ll say it: if the meaning is not in the poem, it is not the meaning of the poem.
The poet may have created the poem, but they did not create the English language (assuming English here). That is, the meanings the word convey are no more the author’s sole work than the dictionary or your mind. AND, from the time of Freud on, we have not assumed the author is aware of all the meaning their own work might show. The author might be the one reader who can’t see what the poem means; that is, the poem might tell more than the author intended.
So, step one, read aloud and slowly, paying close attention to what the words are doing in you. Words are enormous and bleed into each other’s spaces to create new and greater meanings in the minds of readers. In your mind. Words are sounds and as such make music. Music has its own effects on mind & emotion. To be a sensitive reader is to be aware of those effects inside you. The first read, the first several reads, you are reading your interaction with the poem as fully and wakefully as possible.
After, dictionaries, reference works, if necessary...
After that, the fun and most important part: discussion with others (memorization often helps here) in person or by reading their writings about the poem.
Most important answer to this question though: if the meaning is not in the poem, it is not the meaning of the poem. Biography is tertiary at best.