Similar to adding features, you can remove features from a bundle as long as it hasn't been promoted to a downstream environment. To do so, select the bundle, click the 'more' icon and select 'Remove features':
Select which features you'd like to remove:
Click 'Remove features' to confirm.
Once you remove features, the removed features will be reopened against the target environment, just as they would if you'd abandoned the bundle.
Note: You can only remove the most recently added features in order. It's not yet possible to remove an arbitrary feature from elsewhere in the bundle.