"You" can refer to anyone. it can be the reader or the object that is being referred to in the poem. The second case happens when the object is being personified i.e. referring to an object as a person.
for example: you would understand the feeling only if,
in front of your eyes you saw her falling off the cliff.
Here "you" if being referred to the reader
You descend from above, like the tears of the heaven and kiss upon the golden wheat.(these are my own example).
Here firstly the heaven is referred to as a person and the rain as the "person's" tears. And later the rain is being personified to show that it reaches the ground and gently falls upon (kisses) the golden wheat.

So with this you'll be able to understand that the word " you " in a poem can either refer to the reader, one of the characters of the poem or a personification.

I hope my answer helped you.
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good luck