I am a beginner in bonzai, I got my bonzai in a bad conditions,
from what I read in this forum, It seems have several kinds of disease
I attached some photos in order to help me in identification of deseases problems, the leaves have yellowish stains, the back leaves have white bodies, and some brown spots even the young leave got the same stains.

I count on your experience to find solutions

Regards

dont know what it is,but neem oil or insecticidal soap will work .i had an aphid problem with a viburnum and i just wiped the leaves off daily with my fingers to kill them .check the branches and trunk too buggers like to hide everywere