How to change the value of second level variable in Bash?

By using eval:

$ X=8$ Y=X$ echo ${!Y}8$ eval $Y=3$ echo $X3

bash variables pointers

This might work for you:

X=8; Y=X; echo ${!Y}8echo $(($Y=3))3echo $X3(($Y=7)); echo $X7

Here's a couple more ways:

let $Y=4; echo $X4_[$Y=6]=1; echo $X6

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