I haven't given it much thought but my instinct is to keep it on my left hand and add the band in front as that is how I plan to wear them anyways. I'm too paranoid to take my engagement ring off anywhere except at home where it always goes in the same spot so I don't misplace it...😆
If you're undecided or torn on options, you can also ask your officiant on what they recommend. Maybe they can incorporate the engagement ring into the ceremony, whether it be a switch or keeping it in place.
I wore it on my left ringer like I always do. My mom couldn't make it to the wedding and I have one of her rings I wear on my right ring finger so I wanted to wear that to have something from my mom with me on the wedding day.