how to replace 2nd filed of line separated by comma with a value stored in variable

i have a line as below and all fields separated by comma:

I want to replace 2nd filed which is 11:50:21.444 with a value stored in variable "b"

01-01-2022,11:50:21.444,1234543233443,0,0,0,0,1

I tried using sed
cat abc.csv| sed ‘s/$2/$b/’

>Solution :

Any time you find yourself talking about fields you should use awk rather than sed or grep since awk has a concept of fields while the others don’t and awk can do literal string replacements while sed can’t.

awk -v b="$b" '{$2=b; print}' abc.csv