After you complete all the levels. Let's start from the beginning with Episode 1 and run through the doors to level 25 one by one. Don't worry about having to complete the game again because all the doors are already open, you just need to run through it. You can also jump from level 8 -> 10; 13 -> 20 ; 22 -> 25.

At level 25, go to the sewer
It will take you back to level 1

Go to the door on the left below you as shown in the picture, you will be taken to an extra level: level 26

Continue the game and you can collect all the missing achievements.

This area has a total of 8 achievements:

5 achievements +1 key:

Run from lasers

Follow the lasers and get the key

Ninja

Congratulations on completing the 5000 achievement game without using cheats.