How to write a migrate to undo the unique constraint in Laravel?

You have to do $table->dropUnique('users_email_unique');

To drop an index you must specify the index's name. Laravel assigns a reasonable name to the indexes by default. Simply concatenate the table name, the names of the column in the index, and the index type.

This the better way to drop unique. You can use the real column name here.

$table->dropUnique(['email']);