A release that turned out worse than the one before it has to be undone, and undone fast. The rollback is not a rebuild from source, it is a switch back to an artifact that already exists. The whole skill is having that artifact ready before the need for it appears.
About 1 min of reading
Make the rollback one step.
The switch
Before you run it, say out loud what it will print. Then open the answer.
The record
Before you run it, say out loud what it will print. Then open the answer.
Read the first example one line at a time. A line that prints shows what appears on screen; the rest set things up quietly.
How long a rollback takes is a number you want before the emergency. Minutes is a prepared system; an hour of figuring is a system that was never rolled back and never prepared.
What shipped, what the symptom was, what the rollback did, what the fix will be. That record is what stops the same bad release being shipped again next quarter, and it is the only record that survives a week.
The artifact before this one stays available and addressable. A rollback that requires rebuilding from a branch is a rollback that can fail, and a failing rollback is a worse situation than the one it was fixing.
If the new version migrated files, a rollback has to read them. A loader that only reads the new format makes a rollback that breaks on the first open, which is why migration rules are written per step.
The changelog entry and any published claim have to be corrected, not left. A rollback that leaves a changelog claiming a feature shipped is a system whose documentation is a lie about itself.
Each one is defined here on this site. Open the entry for the full definition and the other words it points at.