By default, the program creates a database file in the directory $DATA_ROOT = dirname($_SERVER["DOCUMENT_ROOT"]).
If you're happy with that, then no settings need to be spelled out.
If the default settings don't work, open the file config.php.
Find the lines:
### 1.1. Database
$DATA_ROOT = dirname($_SERVER["DOCUMENT_ROOT"]).DIRECTORY_SEPARATOR;
$DB_DSN = "sqlite:{$DATA_ROOT}sample.sqlite3";
Replace the value of $DB_DSN:
$DB_DSN = 'sqlite:/path/to/sample.sqlite3';
where
/path/to/sample.sqlite3: absolute path to the database file *.sqlite3.
Make sure, that user, under which PHP is run, has write permissions to this file.