Once the time frame you have set for your Kahoot! assignment is over, You can collect all your students' answers as well as how well they did in the assignment by a click of a button.

On the report page, you will find an option under the title "Report options" as underlined above.

Once you click on that it will give you a list of options as shown in the following picture.

You then choose the first option that says "Download report". A report under the format of Excel file will then be downloaded into your Pc.