A notice of enforcement was put through the door for the previous homeowner. What should I do?

Nothing

Bailiffs may only enter homes where the debtor lives,^[1] but if the debtor is no longer living there, he may not enter the address.

A bailiff have no right to enter a property to satisfy himself the debtor does not live there.^[2]

^{[1] Paragraph 14(6) of Schedule 12 of the Tribunals Courts and Enforcement Act 2007
[2] See Neil Tunstall vs Direct Collections Bailiffs Limited (DCBL) and Mr Hussain}