If you have never "purchased" GarageBand before, it won't show in your history. You can fix this by:

When a pop-up appears stating the current version requires a newer OS, click to accept the "last compatible version" offered for 10.11.6. 2. Using a Newer Mac to "Unlock" the Download

However, you can still download a compatible version (typically or 6.0.5 ) using the "Purchased" tab method or official legacy installers. How to Download GarageBand for El Capitan 10.11.6 1. The "Purchased" Tab Method (Most Reliable)

Returning to your El Capitan Mac and following the steps above. 3. Installing GarageBand ’11 (Version 6.0.5)