Laravel-excel: [QUESTION] Reader method [appendRow] does not exist when using Excel template

[Sogl]

Hello!

I load Excel template, than manipulate with data and after that save modified file in default exports folder.
Today I tried to use Laravel-Excel appendRow method, but got an error:

exception 'Maatwebsite\Excel\Exceptions\LaravelExcelException' with message '[ERROR] Reader 
method [appendRow] does not exist.' in C:\OpenServer\domains\drugs.lar\
laravel\vendor\maatwebsite\excel\src\Maatwebsite\Excel\Readers\LaravelExcelReader.php:1275

My code:

$excelFilepath = Storage::disk('templates')->getDriver()->getAdapter()->applyPathPrefix('main.xlsx');

Excel::load($excelFilepath, function($doc) use ($test) {

    //start line
    $rowNumber = 6;

    //test date
    $testDate = Carbon::parse($test->date);

    $sheet = $doc->setActiveSheetIndex(0);
    $sheet->setCellValue('E3', $testDate->format('d.m.Y'));

    $testEmployees = $test->employees;

    //counter
    $employeeCounter = 1;

    foreach ($testEmployees as $employee) {

        $doc->appendRow($rowNumber+1, array($employeeCounter,
            $employee->employeeName
        ));

        $employeeCounter++;
        $rowNumber++;
    }
})->setFilename($downloadkey)->store('xlsx');

I think that's because I can only use reader methods that described here:
https://github.com/Maatwebsite/Laravel-Excel/blob/700eba02f76f2971c81726a4f6a04121c1977e64/docs/import/basics.md

So... how I can use full power of this Laravel extension in my situation?

p.s. Of course, I can write all on the native PHPExcel's methods, but I want to write less code.

[Sogl]

@patrickbrouwers Why this issue closed without any comment?