heilo,coud you first make sure that your standalone instance is started weill,then move to the bin folder under the database on terminal ,from this point you can use the mysql command
One more thing , Another option is to access mysql Database of running openmrs instance using any mysql client like mysql workbench you can as well follow this link
1) make sure you run at the mysql command at the bin folder of the database within the standalone folder
2) On terminal,run mysql -u openmrs -p --port=3316 --host=127.0.0.1
3)Then you can add the password from the run time properties file