The fastest fix is going back.
When a release breaks, get users back to the last working version first. Find the cause afterwards, calmly.
Three Ways Back
Host redeploy
Most platforms can redeploy the previous version in a click.
Git revert
Undo a specific commit, then deploy.
Feature switch
Turn the new feature off without redeploying.
The hard part: data
Code rolls back easily. Database changes don't.
Back up before any change to the data structure.
Decide in advance: “If X breaks, we roll back.”
Roll back first. Debug second.