If you don't have a working OS on the system you can't get access to the setting. So the only way I can think of here is to reset the NVRAM [https://support.apple.com/en-us/HT204063|How to reset NVRAM on your Mac] or using Target Disk Mode [https://support.apple.com/en-us/HT201462|Use target disk mode to share files between two Mac computers] using a second Mac to install the OS from. Here you still need to backwind the date as well. Go into the the Date & Time control panel and disable Set date & time automatically and then alter the date back to a the point the El Capitan was available (2016) then restart and then the installer should work. Just remember to select your system as the target drive.
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The last possibility is to create an OS installer USB to boot up with to alter the date [http://www.macworld.com/article/2981585/operating-systems/how-to-make-a-bootable-os-x-10-11-el-capitan-installer-drive.html|How to make a bootable OS X 10.11 El Capitan installer drive]
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The last possibility is to create an OS installer USB to boot up with to alter the date [http://www.macworld.com/article/2981585/operating-systems/how-to-make-a-bootable-os-x-10-11-el-capitan-installer-drive.html|How to make a bootable OS X 10.11 El Capitan installer drive] and run the installer from it.
If you don't have a working OS on the system you can't get access to the setting. So the only way I can think of here is to reset the NVRAM [https://support.apple.com/en-us/HT204063|How to reset NVRAM on your Mac] or using Target Disk Mode [https://support.apple.com/en-us/HT201462|Use target disk mode to share files between two Mac computers] using a second Mac to install the OS from. Here you still need to backwind the date as well. Go into the the Date & Time control panel and disable Set date & time automatically and then alter the date back to a the point the El Capitan was available (2016) then restart and then the installer should work. Just remember to select your system as the target drive.
The last possibility is to create an OS installer USB to boot up with to alter the date [http://www.macworld.com/article/2981585/operating-systems/how-to-make-a-bootable-os-x-10-11-el-capitan-installer-drive.html|How to make a bootable OS X 10.11 El Capitan installer drive]