How to use CustomTaskChange to migrate data?

I’m new to Liquibase and I cannot find out how my task should be implemented.
I have a already populated SQLite db I want to migrate to a different schema structure. My idea was to

  1. create new tables
  2. loop on old data populating the new tables
  3. drop old tables

Now poit 1 is done easily but I couldn’t find clear instructions on how to do point 2. I thought implementing CustomTaskChange was the right choice (I basically want to loop over rows of one of old tables and, for each row, execute a bunch of inserts on a new table) but I cant figure out how I am supposed to do use it. I can’t find a way to access the underlying connection using Liquibase 2.0.4 and I couldn’t find a clear documentation about how I should perform my task. Is there any documention or could anyone point me to the right direction?