There are two parts to this. You first download a disk image file, which should appear wherever your downloaded files normally go, typically your Downloads folder.
If you can't open the disk image file, then I suggest trashing it and trying again.
Once you've opened the disk image file, you need to copy the QRecall app to your Applications folder. Optionally, you can open the Install QRecall utility application, which will do that for you.
Once in your Application folder, open the QRecall archive and it will install itself.
If you can't open either the QRecall application or the Install QRecall utility, you might have your GateKeeper security settings to restrictive. In your System Preferences, under Security, go to the General tab and make sure Allow apps downloaded from: is set to App Store and identified developers.
If you have anti-virus software installed, make sure it hasn't blocked or sequestered the app.
This message was edited 2 times. Last update was at 19-Nov-20 12:30