You can create an item in a SharePoint list using data from an Excel file that is stored in a SharePoint document library in several ways:

1. Import the data from Excel to SharePoint list: You can use the "Import Spreadsheet" app in SharePoint to import the data from the Excel file into a SharePoint list. Simply upload the Excel file to the SharePoint document library, then use the app to create a new list and map the columns from the Excel file to the columns in the SharePoint list.

2. Use Microsoft Power Automate (formerly known as Microsoft Flow): You can use Power Automate to automate the process of creating an item in a SharePoint list from the data in an Excel file. You can create a flow that is triggered by changes to the Excel file in the SharePoint document library, then use the "Create Item" action to create a new item in the SharePoint list with the data from the Excel file.

3. Use the SharePoint REST API: If you are comfortable with coding, you can use the SharePoint REST API to create an item in a SharePoint list from the data in an Excel file. You can use the API to retrieve the data from the Excel file in the SharePoint document library, then use the "Create Item" endpoint to create a new item in the SharePoint list with the data.

Whichever method you choose, it's important to make sure that the data in the Excel file is formatted in a way that can be easily imported into the SharePoint list. This may involve cleaning up the data, adding or removing columns, or making other changes to ensure that the data is suitable for import.