Change customer sharing from per site to global

I have a Magento store on 2.3.4 with 10 stores and right now the customer account sharing is set to per store. I am wanting to change that to global, if there are customer accounts with the same email in multiple stores is that going to prevent me from doing so or is there a way to merge those accounts? If it does not merge accounts what is the best way to get it to global account sharing?