The easiest way is to delete the data via the ThingsBoard UI, here you only have to select the device and the data can be deleted via the corresponding button:

For other ways to delete, more information would be needed about which ThingsBoard version is in use and which databases are deployed.

It is also possible to set a TTL (time to live) parameter so that data points are automatically deleted after a certain time has elapsed: https://thingsboard.io/docs/user-guide/telemetry/#data-retention