I don't know what you entered as your search phrase but we seem to have a query like that every other month and a simple search with the word "expire" or "expiration" should bring the relevant threads:
Keeping Flying Blue Points from Expiring
Extending the Validity of Flying Blue Miles
How to extend Air France expiring miles
Flying Blue miles expiration date?

In short:

• miles earned up to the last flight can only be extended by an activity that earns XPs (i.e mainly by flying on a miles-earning revenue booking);
• miles acquired since the last flying activity by means other than flying can be extended by a non-flying earning activity.