Hi,
Click “Player Settings” and check if a template is selected. See here: Unity - Manual: WebGL templates
If there are no templates, try to reinstall Unity or look for “Unity template code” online. I found this, but there is probably more if you look for it.
Also please feel free to ask our helpful community of students for further advice over on our Discord chat server.
I hope this helped. 
See also:
- Forum User Guides : How to mark a topic as solved