To sing with the Belting technique in the whistle register it is necessary to use it as for the other registers.
Steps
Step 1. The vocal cords work differently in the whistle register, but this is not a problem for singers
The practical solutions used by singers are the same as those used for the other registers of the voice.
Step 2. DON'T try too hard and hurt your throat
Step 3. Apply the necessary support with the right dose (you need to know what support is and how it works)
Step 4. Open the throat
Step 5. Do not pursue your lips and do not bring your jaw forward
Step 6. Use the Twang technique (nasal voice), it will make things easier for you
Step 7. Pronounce the vowels A, E, I, O and U which are fundamental in the whistle register
Step 8. Do it hard
Belting is as powerful as a cry, but different from this. From 1 to 10 you will need to use a volume of 7-10 as you sustain the note.
Step 9. Never interrupt a note when belting
This means not catching your breath while holding a note.
Step 10. Realize that you will have to practice a lot (you will have to develop your back and abdomen muscles) and sweat a lot BUT remember that you will eventually have to belting the notes naturally
Step 11. Have fun with passion
People sing for passion and fun.