Open Manage | Database | fields
Double click one of these fields to open field options
Select the auto-enter tab
Type the letter x without quotes into the Data box.
Repeat for each of the other fields for which you want to auto-enter the letter x when the record is created.
I got that far myself, but I was worried that it may write over some of the details I already have.
Thanks for confirming that it's the right thing to do.