If you are using a branded PC, such as an HP, you can download the Realtek drivers from the manufacturer’s website.
If you aren’t using a branded PC, you have a few options:
You can get the sound card and try to find a serial number written on it. You can then Google the serial number and get the correct driver that way
You can launch devmgmt.msc from the run command, find the sound card with the missing driver and look at the properties and try to automatically find the driver from the Driver tab
If that doesn’t work, you can go to the Details tab and select Hardware ID from the dropdown. This will give you a hardware ID that you can search Google for to find out exactly what model the card is and what driver to use.
❗ Note: Although 3rd party websites are useful to give you details about your hardware, you should only download drivers from the official manufacturer’s website unless you like cleaning up viruses from your PC