Below is the link on how to change your major from Undeclared to ME. Remember it is always easier to switch out of an Engineering major than to switch into. My advice is always apply for your choice major as a direct admit and UCR does consider your alternate major if you are not accepted to your 1st choice major.
https://student.engr.ucr.edu/policies/requirements/majorchange/me.html
This is from the UCR Website in regards to changing to the Biology major:
Biological Sciences
The Biological Sciences major is currently under a moratorium and no new change of major petitions to this major will be approved at this time.