Change String with Windows Batch Script

Change String with Windows Batch  Script

I have a CSV file that has computer names, usernames
example

computername, Newusername 
comp1,  John
CompX, Alton
....

in each computer C: drive there is a text file (C:\test.txt) that has  a line like this :

aaaaaaaa                  bbbbbbbbbbb        ccccccccccc   -username    username

I want the second username string to be replaced by a string read from the CSV file under usernames ... Note the first username has a dash in front of it and it should stay as it is -username, I need just the second username to be changed.

for instance:
 on comp1 , the line will be

aaaaaaaa                  bbbbbbbbbbb        ccccccccccc   -username    John

 on compX , the line will be

aaaaaaaa                  bbbbbbbbbbb        ccccccccccc   -username    Alton

Thank you