The forgot password module provides this capability and is pretty easy to set up. The documentation for this module describes how to enable create new user. My suggestion is to follow this documentation for setting up this module – https://docs.mendix.com/appstore/modules/forgot-password/ and, once you have that complete, remove the forgot password link in the login page (or alternatively, copy the sign up link and place it wherever you need it).
Have you tried the forgot password module and encountered problems or issues? If so, could you describe the issues you are having in this posting so the community can help you with those?
Hope that helps,
as a beginner this is increadably complex, do not underestimate it.
there are a lot of moving parts that work together on the MX side, but also on the front end side, that being said, it is definitly doable.
Like Mike said, the forgot password module is an awesome place to start, (there are some bugs that might need fixing), but you can search the forum for those fixes (the mapping to email is one i know of)
you will also need to understand basic of setting up smtp.
… and I should probably right a little blog on how to do this at some point hahah :D