The seam allowance is set by default during the drafting process for lines and curves. These values are determined by the Seam Allowance Variables that you choose prior to the draft.
There may be times when you want to change the seam allowance for a particular line or curve. You can do that with the Set Seam Allowance Value tool.
Select the line or curve that you wish to change.
The tool will show you the value that is currently assigned to that line/curve's seam allowance.
Enter a new value to change it. You can also enter a 0 value, which will remove the seam allowance on this line/curve.
You won't see any change. You can use the Properties tool to see the 'data-sa' value or it is visible when you apply a full seam allowance to the pattern.