You cannot log in with FBA now because the database does not yet have users.
There are ways to manage the membership database, which can be managed with IIS. Recommended use of SharePoint FBA Pack (https://sharepoint2016fba.codeplex.com/)
Download and unzip, such as extract to C:\Deploy
Open PowerShell or SharePoint Management Shell (admin mode)
CD C:\Deploy
. \deploy http:\\win-h472cerv00l\ (change to your own Web application)
This script deploys the FBA pack to your farm and site collection. If there is an error, it is because there is no signature. Set-executionpolicy the unrestricted command to remove the limit.
Log in to the site collection with the administrator, you can see the site settings, more management FBA user functions.
Select FBA User Management,
Select New User
Create a new user and join the SharePoint group so that you have permission to log on to SharePoint.
Log out, select FBA login on the login page, log in with the account you just created, log in successfully, and you are done.
Sharepoint 2016 Configuration FBA (iv) Adding users to the Membership database