This repo contains a demo application that showcases the Spreadsheet Validator library, which you can buy here: https://www.import-javascript-angular-xlsx-csv-validator.com.
Download the zip file that you obtained from the Spreadsheet Validator library site, and extract it into a folder of your choice.
In the root of the project, execute npm install.
Finally, execute npm install folder/xlsx-lib. This will install the Spreadsheet Validator library into the project.
Just run ng serve and you are good to go!