1. I have watered the plant
The "have watered" is in the present perfect form. This doesn't go well with a particular point of time such as 'last night' because this is to talk about 'up until now.' (It's in present tense adding the sense/aspect of completion to talk about a past event.)
2. I had watered the plant
The "had watered" is in the past perfect form. This also doesn't go very well with a particular point of time because this is to talk about 'up until sometime ago.' (It's in past tense adding the sense/aspect of completion to talk about something happened before a past event; you need a certain reason to use this form.) [I think theoretically so, but I can't tell if there's other possibilities.]
The perfect form goes well with words such as 'already,' 'recently/just,' 'since,' and 'ever/never'. It has a sense of duration as well as completion; it's also good for talking about a past experience.
(Even though grammar books usually say the 'perfect' is one of the tense form, it is not really about tense, but is called 'aspect' by linguists.) I suspect that the primary use of the perfect form is to add the sense of completion to the non-finite verb (infinitives, participles, and modal verbs) because without it the non-finite verb can not express completion. On the other hand, since such a thing exists people also use it to add the sense of completion to talk about past events, but it ends up saying 'up until now or sometime ago' because it's tenseless by itself. It adds the sense of completion but when added to a finite verb, it makes the meaning vague and is rather optional or subjective.
3. I watered the plant
yesterday last night.
The "watered" is the simple past tense. This form talks about a past event in the perspective as though looking at it from outside; perfective in aspect.
§421.4 In general, the simple past tense is the ‘normal’ one for
talking about the past; we use it if we do not have a special reason
for using one of the other tenses. (M. Swan, Practical English Usage)