A more thorough explanation:

A trademark-application amendment is a proposed change to a registered trademark or an application for trademark registration. There are different types of trademark-application amendments:

This is a minor modification to an existing trademark registration to reflect how the mark is actually used. The U.S. Patent and Trademark Office (PTO) allows an amendment of registration only if it does not significantly alter the character of the mark. For example, if a company changes the font or color of their logo, they may need to file an amendment of registration. The PTO will attach a printed certificate showing the amendment to the registration.

This is a supplement to a trademark applicant's intent-to-use application filed to inform the PTO that a trademark is actually in use in interstate commerce. For example, if a company filed an intent-to-use application for a new product name but later started selling the product, they would need to file an amendment to allege use. The form is titled “Allegation of Use for Intent to Use Application.”

This is an amendment to an application for registration on the Principal Register, requesting that the mark instead be placed on the supplemental register. The supplemental register is for marks that are not yet distinctive enough for the Principal Register but may become so over time. For example, if a company's trademark is descriptive but has acquired some secondary meaning, they may file an amendment to different register to try to get it on the supplemental register.