The default log level is info in Rabbitmq and this guide will instruct you to change it with rabbitmqctl eval command directly.
Below commands will change the different log level.
rabbitmqctl eval 'rabbit_log:critical("Severity = critical").'
rabbitmqctl eval 'rabbit_log:error("Severity = error").'
rabbitmqctl eval 'rabbit_log:warning("Severity = warning").'
Please refer to below guide for more detailed information:
https://www.rabbitmq.com/docs/logging#log-levels