As stated by @musab-dogan, it is worth noting to change your password. To change your password, you can use the command below:

/usr/share/elasticsearch/bin/elasticsearch-reset-password -u elastic

When you also applied changing your password, make sure you do the following:

$ echo "<your-new-password>" > /etc/elasticsearch/certs/keystore.tmp 
$ chmod 600 /etc/elasticsearch/certs/keystore.tmp 
$ chown elasticsearch.elasticsearch /etc/elasticsearch/certs/keystore.tmp 
$ sudo systemctl set-environment ES_KEYSTORE_PASSPHRASE_FILE=/etc/elasticsearch/certs/keystore.tmp

If you want guidance on installing Elasticsearch, please check if this article is helpful for you especially with your experience on password issues.