You can find the Setup-Instructions here. Carefully follow the instruxctions. https://www.b4x.com/b4a.html#Installation
You also can watch this Video as it describes it clearly.
Start with a new Blank folder like you see in the Video.
I went through your dilemma; patience will be your friend. You used the folder icon at the top of the sdkmanager page to set the path to the sdkmanager.bat file right? That .bat file is key. After that, searching the rest of the AVD manager information might present you with a hangup and solution; I'm hoping.