src/TableBlueprint.php
public function alterIndex(array $columns, array $options): self
    {
        return $this->addOperation(
            new Operation\Index\Alter($this->table, $columns, $options)
        );
    }
public function alterIndex(array $columns, array $options): self
    {
        return $this->addOperation(
            new Operation\Index\Alter($this->table, $columns, $options)
        );
    }
Example:
$table->alterIndex(['email'], ['unique' => false]);

@param array $columns
@param array $options
@return TableBlueprint