Sequential Read With Update To Status Flag?

Reading a sequential flat file (which is working) but now I need to add code to update the status flag (setting it to ‘Y’ position(7,1)) before I close the file and not sure how without defining the fields.

try
{
tFile = getTFileName();
System.out.println("File Name: " +tFile);
ukarf = new ZFile(tFile, options);
while(!EOF) {
int bytesRead = ukarf.read(buffer);
System.out.println("Record read: " +new String(buffer,0,9,"IBM-1047"));
if(bytesRead == -1)

[code]....