Do you remember what to do?
No, I have forgotten. (This is the correct answer because you forgot earlier, and still do not remember)
Have you seen Pete recently?
I saw him last week. ('Last week' tells you this is past tense, so you cannot use a present perfect)
You look tired.
I have been working hard. (There is evisdence now of something which as happened recently, so you need present perfect continuous.)
What did you do for your holidays last year?
I went to France. (We are talking about last year, so the past tense is needed.)
I'm sorry it is dirty.
You should be. I had just cleaned it (You use present perfect for when an action in the past is still true. It is not clean now, so use a past tense.)
What are you looking for?
I've lost my watch. (I lost my watch in the past and still have not fount it - therefore present perfect.)