The phrase "to find the nipple" means discovering the source or solution to a problem or difficulty. It is often used in a humorous or colloquial manner. Full definition
If you do not find nipples, your hamster may be male. (wikihow.com)
In addition, you may also find your nipples become more sensitive making it painful to breastfeed. (breastmilk.com)
Nothing can be more frustrating than finding a nipple ring that belongs to the bottles that are dirty in the sink instead of the clean ones on the counter. (myorganicformula.com)