Vauxhall Insignia keyless version. Can't remember model. But local garage that did the service wasn't sure how to reset it either. They said it may be a dashboard fault, hence I took it to Vauxhall dealer. They charged ~£80 and I found out that he plugged in laptop to reset it rather than fix the dashboard.
However managed to reset it myself after reading this thread. As it's keyless start, you can't access the oil options without the engine being started. I selected the reset while holding break and clutch when I confirmed reset. Still no change. However after stopping and starting engine again, it came back with 100% oil life. So not sure what the exact sequence is required.