Tim,
Please refer to this thread: Guide to Getting Useful Support
…we need some more details in order to provide assistance. (note: the forum isn’t official Zwift support, just users like you sharing their knowledge)
I’d suggest ensuring your trainer firmware, and all app and companion software are up to date. Latest versions listed here: What are the latest Zwift Game and Zwift Companion app version numbers?
If you could note what specific device (brand, model, year, OS, RAM, CPU) you have, that’d help.
As other noted, it’s unlikely you’ll be able to edit an existing activity but you could start another ride to accumulate kilometers, or join another Festive 500 event if you want credit for one of those.