Requirement to be a QMS consultant

Do I need to be certified, in some way, to help them design and implement a Quality management policy that will eventually be audited by an ISO auditor?

Answer
There is no legal requirement for an ISO 9001 consultant to be certified in any way.

The following material will provide you information about quality policy:
- Article – How to Write a Good Quality Policy - https://advisera.com/9001academy/blog/2014/03/25/write-good-quality-policy/
- ISO 9001 document template: Quality Policy - https://advisera.com/9001academy/documentation/quality-policy/
- Free course – ISO 9001:2015 Foundations Course - https://advisera.com/training/iso-9001-foundations-course/
- Book - Discover ISO 9001:2015 Through Practical Examples - https://advisera.com/books/discover-iso-9001-2015-through-practical-examples/