If you have Couchbase (3.x) installed, and you forget the administrative password or you want to change it, you can go to Couchbase directory, and then reset it
$ cd /opt/couchbase/bin
$ sudo ./cbreset_password
Please enter the new administrative password (or <Enter> for system generated password):
Running this command will reset administrative password.
Do you really want to do it? (yes/no)yes
Resetting administrative password...
Password for user Administrator was successfully replaced.