How to replace values ​​in SQLlite table?

Question

SQLite

In How to make a query correctly so that in the entire table tab1 to replace NULL values ​​with 1 is acceptable.
I re-read, I can not fully understand these requests.

Answer 1

UPDATE tab1 SET fieldName = 1 WHERE fieldName IS NULL;

Answer 2

I try an example like this:
you need it like this:
it turns out like this: