The most common approach is to add versions to the events. The good thing is that with event sourcing, the exact cutover and lifetimes of these schema versions can be known (and even recorded as events themselves).
Downstream apps and consumers that don't need to be compatible with the entire timeline can then migrate code over time and only deal with the latest version. You have to deal with schemas anytime you have distributed communications anyway, but event sourcing provides a framework for explicit communication and this is one area where it can make things easier.
For me an issue, not usually made explicit, is that those benefits seem to require a pretty stable business and a stable application landscape.
Why? Because a changing business requires changes to the Events. Since a change in an Event requires that all consumers to be updated, immediately or at the schema version deprecation, the cost of change seems to increase faster in comparison to an application landscape without event sourcing. At the same time, the cost to know who needs to be changed also grows since "any" application can consume any Event.
An stable application landscape also seems to be required because if the number of an Event consumer grows quickly the ability to update, and deprecated schemas, seems to be related with the number of Event consumers (which require update).
If your org is anything like mine, mostly things (data) are "additive" onto the existing structure. When you want to deprecate something, you can notify all the consumers like a thirst party would, if you were going to change something enough. But this later happens much rarer for us, though tends to leave traces of technical debt....
Downstream apps and consumers that don't need to be compatible with the entire timeline can then migrate code over time and only deal with the latest version. You have to deal with schemas anytime you have distributed communications anyway, but event sourcing provides a framework for explicit communication and this is one area where it can make things easier.