Hi Paul,
You can try the following workflow in order to access the survey submissions from the sqlite database.
1. Open the sqlite file in DB Browser for SQLite
2. Inside of this database is a single table called "Surveys"
3. If you select the browse data tab, you can see that all submission data is stored in the "data" field as JSON.
4. You can export the survey table as a CSV file by selecting File > Export > Table(s) as CSV File...
5. This CSV will require cleaning up - the most important thing here is the data column which will need to be parsed and cleaned up to match your survey's schema. You can use the following json to csv converter to clean up the data field.
https://konklone.io/json/
6.Once the schema of the CSV matches the Survey's hosted feature layer you can append the CSV to the survey .
Best,
Marisa