If you are using Desktop Then do following steps:
1.Download Zip file of extension.
2.UnZip That file you will get one folder with extension name:
3.Copy paste that folder into following path:
Refresh qlik sense application
If you are using qlik sense server then try this:
2.open QMC and then select extensions from Start.
3.Import and select the downloaded extens.zip
refresh qlik sense