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We are not the biggest fans of doing index calculations on uncalibrated imagery. Yes, the create outputs that look right but they really don't mean anything and can't be compared with data taken at other times unless they are both properly calibrated.
Since we deal primarily with images straight from drone cameras we haven't added any ag index capabilities beyond NDVI because we don't want people thinking it is actually accurate data. You can read more about this here:
https://support.dronesmadeeasy.com/hc/en-us/articles/206003636-NDVI-Processing
If you do still want to dig in to playing with the channel data you can use QGIS's raster calculator feature to make any index equation you could want.
https://opensourceoptions.com/blog/remote-sensing-with-qgis-calculate-ndvi/
https://www.youtube.com/watch?v=vpxVkYaWMno
