awk 'BEGIN{ FS="," }
{
    s=""    
    for(i=1;i<=NF;i++){        
        if ( $i !~ /,/ && $i !~ /\"/ && !f ){
            printf $i","
        }
        if (f && $i ~ /\"$/){
            printf s $i","            
            s=""
            f=0
        }
        if(i==NF){ print ""}
        if ( $i ~ /^\"/ && $i !~/\"$/)  {
          f=1
          s=$i          
        }
        if (f && $i !~ /^\"|\"$/ ){
          s=s $i
        }
    }
}' file | sed 's/,$//'

# more file
rohan,rahul,"kun,,al","sw,a,ti"
rohan,rahul,"k,un,al",swati
rohan,"rah,ul",kunal,swati
"ro,han",rahul,kunal,swati
rohan,rahul,kunal,swati
# ./testnew.sh
rohan,rahul,"kunal","swati"
rohan,rahul,"kunal",swati
rohan,"rahul",kunal,swati
"rohan",rahul,kunal,swati
rohan,rahul,kunal,swati