1. cd your_redmine_installation_dir/plugins
2. git clone -b main https://github.com/conveniencable/redmine_excel_connector
3. Current Directory is your redmine installation directory
   bundle exec rake redmine:plugins:migrate RAILS_ENV=production
4. Restart redmine

Or

1. Download zip file from HERE
2. cd unzip and them copy it to your_redmine_installation_dir/plugins
   the unzip directory name must be "redmine_excel_connector" which contains sub directory app, config, ...etc
3. Current Directory is your redmine installation directory
   bundle exec rake redmine:plugins:migrate RAILS_ENV=production
4. Restart redmine