Step 1, stop auth if existed
Mac
vi /usr/local/etc/mongod.conf
comment these two lines.
# security:
# authorization: enabled
Step 2, restart mongodb
Mac – brew
$ brew services list
$ brew services restart mongodb-community
CentOS
$ sudo service mongod start
$ sudo service mongod restart
$ sudo service mongod stop
Step 3, modify the password
$ mongo
Mongo > use admin
Mongo > db.changeUserPassword("accountUser", passwordPrompt())
Step 4, login with the password