A W-9 is used to provide your correct Taxpayer Identification Number (TIN) to the person or business who is required to file an information return with the IRS, usually to report income paid to your organization.
You can fill out a W-9 form for your organization using this form:
https://www.irs.gov/pub/irs-pdf/fw9.pdf
You will need to know your organization's EIN for Part 1 of the form, see
https://togetherwork.zendesk.com/knowledge/articles/4411630775437/en-us?brand_id=360006995471.