Hi,
as you can see in the images you posted, apart from a tempered scale, six alternative tunings are available:
Pythagorean
Werckmeister III
Werckmeister IV
Werckmeister V
1/4 meantone
Harmonic
To change the tuning, get into the config menu, press the ‘Scale’ key and then select the scale with the lower keys.
It is unfortunately not possible to send custom tunings to the Juno-66. This was a feature we wanted to build in, but which failed due to various technical reasons and incompatibility problems with the software ‘scala’