Volume Error upon Update

[Sp0824]

I was recently forced to update my 2012 MacBook Pro A1278 in order to connect my phone to iTunes. However, the update didn’t work and now my MacBook upon turning on loads halfway and crashes. I press comman+r to get to disc utility (I don’t have any time machine saves). I run First Aid on all the options on the left and all run to completion except the first aid on Macintosh HD which gives the error in photograph attached. It says First Aid process has failed. If possible back up the data on this volume. Press done to continue. Details section says “The volume Macintosh HD could not be verified completely. File system check exit code is 8. Updating boot support partitions for the volume as required. File system verify or repair failed. Operation failed.” How do I go about solving this issue? I have an external so save data but how can I do that from Disk Utility? Thank you in advance!