You need to go through all the levels of the fifth board and do all the objectives. Here is a video made by myself showing you how to handle the different missions.
If you only need a few levels, you can watch the specific video guide below.
Level 5-1 :
Level 5-2 :
Level 5-3 :
Level 5-4 :
Level 5-5 :
Level 5-6 :
Level 5-7 :
Level 5-8 :