Help in creating the most simple Athena UDF

Hi, could someone please give me an example in using a very simple UDF. From that simple UDF I could make it a more complex one, but I just need a very simple start in returning a substring from a database field. I have 2 problems:

1. How to define a correct UDF in my query. My query now is:
   USING EXTERNAL FUNCTION test(ID VARCHAR) RETURNS VARCHAR LAMBDA 'test'
   select test(ID) FROM "BibleLinkDynDB"."default"."bible_link_statistics" limit 10;
   ID is the database field.

2. How to use the input from the UDF in the lambda function. Based on the lambda template my function looks like this:

I know this is not correct. I don't now how to get and process the input string because I think event is an object.

If someone could please give me a hint or a simple example, then this beginner would be very grateful.

kind regards Reyer