Student or Learner
A : "I have been thinking a lot about this... "
B : "Okay, before you say anything, I wanted to give you..this (a muffin)"
This is a script of USA sitcom "How I met your mother". The script could be wrong, but the script says B said past verb "wanted" instead of "want" there. I think want is right. Could you help me for that one?
There's nothing wrong with the original sentence.
The idea is that he "wanted" to do this (previous desire) and now he is doing it.
Saying "I want to do this" is grammatically OK, but it's more natural to express that you had the desire and are now fulfilling it than it is to announce that you have the desire in the present tense.