How to get to the varable in a list

Hello,

I have a list "lis" as the following:

$"1"
  x1 x2
4  3  1

$"2"
  x1 x2
3  3  2
5  3  2

$"3"
  x1 x2
2  3  3
6  3  3

How do I get the x1 varible?  for example ss"1"

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