How to use Maatwebsite Excel import in Laravel Restful API

Initially I have full Laravel Application. In it I use Maatwebsite-3.1 to import from Excel into the database as shown below:

class GradesImport implements
    ToCollection,
    WithHeadingRow,
    SkipsOnError,
    WithValidation,
    SkipsOnFailure
{
    use Importable, SkipsErrors, SkipsFailures;//, SkipsFailures, SkipsErrors; 

    public function collection(Collection $rows)
    {            
        foreach ($rows as $row) 
        {
            $this->gradelevel = $row['grade_level_code'];         
            HrEmployee::where('company_id', auth()->user()->company_id)
                ->where('employee_code', $row['staff_id'])
                ->where('email', $row['official_email'])     
                ->update([
                    'grade_level_id' => $this->getGradeLevel(),
                ]);
        }
    } 
    
    public function rules(): array
    {
        return [
            '*.employee_code' => [
                'required',
                'min:2',
                'max:20',               
            ], 
            '*first_name' => [
                'required',
                'string',
                'min:3',
                'max:50'               
            ],  
            '*last_name' => [
                'required',
                'string',
                'min:3',
                'max:50'               
            ],            
            '*grade_level_code'            => 'required',  
            '*official_email' => [
                'required',
                'email', // official email
                'max:100',               
            ],            
        ];    
    } 
    
    public function customValidationAttributes()
    {
        return [
            'company_id'                                => 'Company',
            'grade_level_code'                          => 'Grade Level Code',
            'employee_code'                             => 'Staff ID',
            'first_name'                                => 'First Name',
            'last_name'                                 => 'Last Name',            
        ];
    }
    
    public function getGradeLevel(){
        if(!empty($this->gradelevel) || !$this->gradelevel){

            return Grade::where('grade_level_code',$this->gradelevel)->where('company_id',Auth::user()->company_id)->pluck('id')->first();
        } else {
            return 0;
        }
    }  
    
    public function headingRow(): int
    {
        return 1;
    }         
}

The above code is working fine in plain excel.

But Now I'm to convert it to Laravel Restful API and then use Angular-11 as the frontend.

How do I achieve this with the same code? Or is there any better way?

Thanks