Question: Changing values of table

I would like to extrapolate some values from a table:

What I have now is something like this: 

table [
(1,100)=1,
(1,200)=12,
(2,300)=33,
(3,100)=1,
(1,300)=43,
(3,200)=52,
(2,100)=31,
(2,200)=22,
(3,300)=3,
(4,...)=...]

I would like to have a table with the same value in the first position with changing the second value, for example:

table[
(2,100)=31,
(2,200)=22,
(2,300)=33,
(2,...)=..]


How can I do it?

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