I have SQL standard 2019 key but I do not have iso or installation file to install it.
Please guide me where I can get 2019 standard edition iso file. I tried Microsoft download page but getting only evaluation / developer / express edition iso file.
If I recall correctly, the license key will determine what edition is installed, but the download media is identical for Developer, Enterprise, and Standard Editions. Suggest you try installing with your product key, and download the installation media if you haven't already.
After install, you can run SELECT SERVERPROPERTY('Edition') to get the actual edition that's running, and if it's not Standard, then you'll need to contact Microsoft to get the correct ISO.
Otherwise, if you have an MSDN or Visual Studio subscription, you should be able to get a marked Standard Edition ISO from their download sites.
You are supposed to contact your software provider for the Standard Edition media, and/or from your MS licensing account.
If you want to try installing the DEV edition and entering your license key for that. If that fails you'll need to contact Microsoft or whoever you got the license key from.