Hello. You did not specify which poem the question refers to, which makes it impossible for this question to be answered. However, I will explain to you how you can answer it. I hope this can help you.
To start a diary entry it is important that you first read the poem and understand what the speaker is saying. In a poem, the speaker is the narrator, that is, it is the voice that is telling the poem to you as you read it. You must identify in the reading what is the problem that the speaker is presenting. After that, you should put yourself in the speaker's shoes wondering how you would write about this problem in a diary. Remember that the diary is a personal narrative where the narrator has complete freedom to express his deepest feelings. In that case, you should talk about this problem in a personal way, showing how it affects you and how you feel about it.
It is important to remember that at the beginning of a diary entry, you must present the date, day of the week and time when the entry is being written.