Open mtaserver.conf
And find this:
# Admin
# Required: No
# Purpose: Defines all the people in-server who can rcon_login to admin
# Format - Admin
# Notes:
# admin-level must not go above 5
# Names and passwords are case sensitive
#Admin Default password 5
Change it to
# Admin
# Required: No
# Purpose: Defines all the people in-server who can rcon_login to admin
# Format - Admin
# Notes:
# admin-level must not go above 5
# Names and passwords are case sensitive
#Admin Default password 5
Admin n00b[RO] 5
Start your server and open the console ( F8 ) and write rcon_login