These are two separate issues.
A Certificate of Analysis (COA) is a document that shows the testing of your finished good as compared to your established specifications in certain subjective and objective areas such as appearance, odor, viscosity, and so on. This requires the appropriate testing equipment and for the most part some background in testing. As such, unless you have the credible talent within your organization, you will need to outsource this to a testing service. The Society of Cosmetic Chemists (SCC) website lists providers of this service under referrals.
Now, a Certificate of Good Manufacturing Practices is issued by your companies Regulatory person and it states that you are following Current Good Manufacturing Practices. At minimum, I would state that this would require a QA/QC Program as well as SOP’s outlining your standard practices and procedures. Many smaller crafters under estimate the sophistication and documentation standards which should be performed in Cosmetic Manufacturing and this is the point where they get bitten. cGMP is a broad topic and I would recommend reading up on it;
https://www.fda.gov/cosmetics/resourcesforyou/industry/ucm388736.htm
https://www.fda.gov/Cosmetics/GuidanceRegulation/GuidanceDocuments/ucm2005190.htm
https://www.amazon.com/Good-Manufacturing-Practices-Cosmetic-Handcrafters/dp/0979594545
The last reference is a book written by Marie Gale. Anyone who has worked with cGMP in a Commercial setting may find it a bit simple, but it is certainly a good starting point.
In summary, if the Forum requires this and you don’t have these programs in place, you aren’t ready to sell in that market and you have some homework ahead of you.