If you mean turn off pre boot authentication by storing the key on the drive (thus negating the point of encrypting) thats an option in the policy within epo. Searching for autoboot in your docs should find the right section.
There's also an option to turn pre boot authentication off, by leveraging TPM which doesn't reduce the security level (like the standard "autoboot" option).
It will require the device to have TPM 2.0 (if MDE 7.1.0 is used) or TPM 1.2 (if MDE 7.1.1 is used).
Note that it doesn't turn off pre boot completely, but as long as the system integrity (per TPM) remains as is, you won't be prompted for a pre-boot password.
Take a look at DE v7.1 FAQ: TPM AutoBoot