Returning a value based on the last edited cell in a row

Hi

Please can you help me. I have basic excel knowledge but need to set up a covid register for lateral testing in our schools. You will see from the spreadsheet the columns and rows I have. The yellow highlighted columns I am hoping someone can help with auto populating them based on formula but I have no idea how to do this.

I will be populating cells (hopefully) with the letter N for Negative. The tests will happen either daily or weekly so all staff will have different dates - therefore I want a cell to return the very last date of that member of staffs test result so I can filter that column quickly.

I also want to autofill the last test result in a column.

I've attached my very basic spreadsheet.