How to resolve unknown licenses for compliance?

When I take a look at the License Compliance section of my project, I see a number of upstream components listed with unknown as their license. A clear example is Jinja2:

unknown Jinja2 (2.11.3)

When I do a quick search, I see Jinja2 is marked as using BSD License (BSD-3-Clause): Jinja2 · PyPI

So, how do I let GitLab know this is a known license?