Firstly, download the trial version of Excel Import and install it to your SharePoint server.

In the Central Administration, click the WEB APPLICATIONS, then click Manage Features.

When Manage Web Application Features dialog appears, set Status of Excel Import Timer Job as Active as following.

This feature will enable a timer job runs in the background to check job and import data from Excel spreadsheet into the SharePoint list.

Click OK to save the settings.

Navigate to the Customers list.

Under ITEMS tab, click Manage Import Job command in Import & Export group.

When Manage Import Job dialog appears, click Create New Import Job.

Then in the Import Excel Spreadsheet from Remote Server dialog, enter the URL of Excel spreadsheet Customer.

Click Next button for the next steps.

And then type the user name and password to access the Customers.xls file.

Click Next button for the next steps.

Then you will be navigated to the Import Excel Spreadsheet from Remote Server dialog. In this dialog, configure the following options.

In the Import Job Name section, specify a name for this job such as Job-1.

In the Sheet section, select Sheet1 to import and select Skip header row in Excel option.

In the Column Mapping section, select these list columns and map with the columns in Excel.

In the Filter section, because we want to import all rows of Excel spreadsheet, unselect Import from row [] to [] option.

In the Import Options section, select Check duplicate records when importing option, and specify Customer and Contact as key as following.

In the Recurring Schedule section, select Manually option to run the job by manual.

And click Save button to save the settings.

And then, you will find that Job-1 is created in the Manage Import Jobs dialog as following.

Because we specify the Schedule as Manually, click icon to run the Job-1.

Wait for the job run complete and click Close button.

And then you will find that the rows of Excel file Customer have been imported into the Customers list as following.