I know to teach is 教え, but I'm not sure how to use the passive form. Google Translate gave 彼が教えしたいです, but that seems he wants to teach (sb). How about 教わたい?
教え is a noun meaning teaching. What you want is verb 教わる : おそわる (to be taught).
Note that there is another similar verb which is 教える : おしえる (to teach).
Although it's grammatically correct to turn 教える into it's passive form 教えられる, it's more common and preferred to use the 教わる instead
I want to be taught by him.
In this case we can use 教えて since by adding もらう, it modified the verb into (receive action[verb] from someone) :
I want (to receive a favor of being taught) by him