Hi Vijayananda,
Unfortunately, we cannot undo the import of updates to existing records.
We can only delete newly created records that are imported.
So we have to pay attention to two things:
1. Is this extra column a field in the entity? In other words, is the name of the column the display name of the field?
If so, an update to the field is imported to take effect.
If not, then the column update will not take effect.
2. Is this field of the extra column enabled for auditing?

If so, we can see the value of the field before it was updated, so that we can manually undo it according to the audit.
Go to Settings > Auditing > Audit Summary View, double click to open this audit record. We can see the value of this field before the update.

For more information on auditing, please see this article:
[View:https://crmbook.powerobjects.com/basics/data-management-in-microsoft-dynamics-crm/auditing-in-microsoft-dynamics-crm/:320:50]