awk or sed change field of file based on another input file

I have a sparse matrix ("matrix.csv") with 10k rows and 22 columns (1st column is "user", and the rest columns are called "slots" and contain 0s or 1s), like this:

user1,0,0,0,1,0,0,0,1,0,1,0,0,...,0
user2,0,1,0,0,0,0,0,0,0,0,0,1,...,0
user3,0,0,0,0,0,0,1,0,0,0,1,0,...,0
...

Some of the slots that contain a "0" should be changed to contain a "1".
I have another file ("slots2change.csv") that tells me which slots should be changed, like this:

user1,3
user3,21
...

So for user1, I need to change slot3 to contain a "1" instead of a "0", and for user3 I should change slot21 to contain a "1" instead of a "0", and so on.

Expected result:

user1,0,0,1,1,0,0,0,1,0,1,0,0,...,0
user2,0,1,0,0,0,0,0,0,0,0,0,1,...,0
user3,0,0,0,0,0,0,1,0,0,0,1,0,...,1
...

How can I achieve this using awk or sed?

tried

awk -F"," 'NR==FNR{user=$1;slot2change=$2} NR!=FNR; /user/ slot2change==0{print $0} ' slots2change.csv matrix.csv 

but I feel I am still far from a correct command…

>Solution :

Like this:

awk 'BEGIN{FS=OFS=","}
    NR==FNR{arr[$1]=$2;next}
    NR!=FNR {for (i in arr)
        if ($1 == i) {
            v=arr[i] + 1
            $v=1
        }
     print
    }
' slots2change.csv matrix.csv