In which chapter of 1984 does the quote about controlling the past appear?

It is in Part One,
Chapter Three of  that you can find the following quote about controlling
the past:

"Who controls the past," ran the Party
slogan, "controls the future: who controls the present controls the past."

To illustrate the meaning of this quote,uses the example that
Oceania is at war with Eurasia. While the Party claims that Oceania has always been at war with
Eurasia, Winston can clearly remember a time, four years ago, when Oceania and Eurasia were in
alliance. This knowledge, however, exists only in his "own consciousness" because the
Party has rewritten history so that this alliance never happened.

It is this
manipulation of the truth, or "reality control" as Winston calls it, that contributes
to the Party's everlasting and totalitarian power. It can make people believe whatever it tells
them because it rewrites history accordingly.

It is also worth looking at the
text from Emmanuel Goldstein's book which appears in the last chapter of Part Two. In the
following quote, Goldstein further explains the Party's control of the past:

"The past is whatever the records and the memories agree upon.
And since the Party is in full control of all records and in equally full control of the minds
of its members, it follows that the past is whatever the Party chooses to make
it."