I have a 501c3 setup in the US but would like to operate in Nigeria. Are there any specific guidelines?

A 501(c)(3) organization is a tax-exempt organization in the United States. Among this category, the most common are 501(c)(3) organization, which are most commonly non-profit charitable organizations. A 501(c)(3) organization is exempt from federal income tax, and thus also allows donors to reduce their taxable incomes. 501c3 exemptions are applicable only in cases of organizations doing religious, charitable, literary, educational and related activities.

Note that not all registered nonprofits are tax exempt. Only those who get 501c3 status are.

Interestingly, nonprofit organisations registered or located outside of the United States can also apply and attain the nonprofit status. The advantage of this status is that your organization will be eligible to receive grant funding from a more number of US donors, private foundations and governmental agencies. Several of these donor agencies actively seek out to fund only 501(c)(3) nonprofits.

As for the guidelines are concerned, the 501(c)(3) nonprofits should function has a public charity or private foundation. It should not get involved in political activities and its actions should be charitable in nature. Section 501(c)(3) of the tax code lists the following charitable purposes: educational, literary, scientific, religious, public safety testing, amateur sports competition, and prevention of cruelty to children and animals.

For more details, please refer to https://www.irs.gov/pub/irs-pdf/p557.pdf

Also read: https://www2.fundsforngos.org/featured/how-to-set-up-501c-3-non-profit-in-united-states-and-what-are-its-advantages/