Here's a good article on myths about jaundice - big NO to sunbathing, nurses and doctors have been advising against this; herbal bath may not help too. Just follow instructions of medical professionals https://www.youngparents.com.sg/pregnancy-baby/3-myths-about-jaundice-newborn/?slide=1
Sunbathing may help, and also drinking more milk to pass bilirubin out of their system. Bathing don't sound too scientific to me as jaundice is caused by accumulation of bilirubin levels as their livers are still to premature to cope with the breakdown of red blood cells
My baby had jaundice previously what I did was sun bathing her use a cloth to cover the eyes and do it for a week around 8am for 5 min take a break of 2 3 min and do it again for 3x. After 1 week jaundice level drop alot. Hope it can help you!