if rebirth/reincarnation is true then what is your first birth/incarnation? I think the question is clear so no further explanation is needed.
Do you think someone might have asked that question before?
According to Access to Insight, many of the suttas include the following quote,

At Savatthi. There the Blessed One said:

&quot;From an inconstruable beginning comes transmigration. A beginning point is not evident, though beings hindered by ignorance and fettered by craving are transmigrating &amp; wandering on.


In other words the &quot;first&quot; is not evident (or, I'd read that as, it's not evident that there is a first).