re download android studio
because it will first open setup wizard and download all that stuff for you
if you dont get it
then download sdk manually
visit google's devolper page and
find android studio download page
going downward that page you will find sdk tools
if you still face error then adress to stack overflow
you will also find many sites giving you android sdk support
I have used Android Studio previously, and have encountered the same issue.
I think the way I fixed it was uninstalling Android Studio and reinstalling it, but make sure all of the needed documents/files are selected to download.