You may have found that since updating to Windows 10 Build 1903 (19H1) on your Dell System that the AT&T sim card is not working.
Troubleshooting has identified this as an incompatibility issue with the Windows Mobile Broadband Interface Module (MBIM) and the PCIe driver.
This issue can be confirmed by viewing the Windows Device Manager. Look for the DW5820e Device YB Error code #10.
Figure.1 AT&T DW5820e SIM card error
Updating the latest WWAN driver version on the computer will help resolve the issue. To download and install the latest driver:
Browse to the Dell Drivers & downloads page:
Ensure you have the correct system set
Select the Operating System
Under Category, select Modem/Communications
Locate the latest 5820e WWAN driver (Version A03 or newer)
Click Download and save the file to your computer
Open File Explorer and browse to the location where the downloaded file is saved
Double-click the driver setup file and follow the on-screen instructions to complete the installation process