Replaced BIOS battery lost settings

I had to replace the BIOS battery on dell optiplex 9020 hackinstosh and I lost all my BIOS settings and now when it boots I get "no bootable devices". What are the settings that need to be selected? Under settings>general>boot sequence>mac OS X is selected. Do also need to select UEFI? because neither are working? Do I need to have a USB with mac osx and reinstall?

submitted by /u/WorkingVomit
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