Most poems, at least short ones and non-dialogues, should stick to one voice, tense, and point of view. It shouldn’t swing between first person singular and second person and third person formal. It should have unity. It should be cohesive.

The exceptions come with longer poems or dialogues. In these exceptions, there are ways to signal the reader of the change in point of view. One way is to have each voice separated into a different stanza in a dialogue format. Another is proper use of quotation marks. There are many more. The point is to ensure that if there are separations in the point of view, that the break-point is clear.