You cannot download the App Store. It is built in, cannot be deleted, and there is nowhere to download it from so not sure what exactly you did.
If App Store is not visible on any Home Screen, look for it in your App Library. click here ➜ Organize the Home Screen and App Library on your iPhone - Apple Support
If its not there either, then verify you have not set up Screen Time and Parental controls and disabled it in Settings ➜ Screen Time ➜ Content & Privacy Restrictions ➜ iTunes & App Store Purchases ➜ Installing Apps. Make sure its set to Allow.
If that is set to Allow, then there may be some corporate profile disabling it. If you have an office or school email account installed on the iPhone it may prevent the use of App Store as a policy. You would need to contact the IT department at your work or school if that is the case.