Before you file
Read the DMCA policy. You will need the listing link, proof you own the work, your contact details and a typed signature.
Filing a false notice can make you liable for damages. If you are a seller whose listing was removed, see counter-notices.
Is it actually infringement?
Similar style. A matching look, palette or idea is not a copy. Only the work itself is protected.
Licensed use. A buyer using your asset inside their product is usually within licence.
Trademark. Logos and brand names are a trademark matter, not a DMCA one.
Same stock source. Two assets built on the same stock or public-domain source are not infringing.