The way this is done depends on your DBMS, however generally speaking there are the following steps:

1. Create a Dump File out of your SQL-Database. A dump file contains all sql-statements needed to recreate that same SQL-Database on another machine.
2. Check if your source DBMS does contain Syntax not supported in SQLite. The documentation for SQLite https://sqlite.org/lang.html is the main source for this task.
3. Craft the SQL-Dump so that it only contains SQL-Statements supported by SQLite. Note that you might loose some functions compared to the source database.