A 60-second screen recording of Pearspark doing exactly this in a sample school, and the same 6 steps written out below in the labels you'll see on screen.
1Click Classes under Learning in the sidebar, open your class, and click Gradebook
2In the grade grid, click the student's cell under the assignment
3Type e (for excused) and press Enter
4The cell shows the excusal instead of a score, and it no longer counts against the student's average
5Note the legend under the grid: 'e = excused · blank = ungraded'
6To undo, click the cell and type a score — entering points replaces the excusal
Part of Gradebook, report cards & transcripts
Enter grades in a spreadsheet-style grid, post them once, and watch report cards and transcripts assemble themselves — plus the What-If views families use on their side.