There are 2 things - 3 things - required to access the
Tomcat admin webapps.
1. They must be installed (Some Tomcat versions do not include them in the base download).
2. You must have enabled a security Realm in the TOMCAT_HOME/conf/server.xml file. By default, no realm is available, but commented-out samples are present.
3. You must have roles defined and assigned to the admin user(s) - who, of course, also need to be defined.
Most commonly, people fail at item #2.
The secret of how to be miserable is to constantly expect things are going to happen the way that they are "supposed" to happen.
You can have faith, which carries the understanding that you may be disappointed. Then there's being a willfully-blind idiot, which virtually guarantees it.