The plural form is to add an s directly to the end of the word.

According to English grammar rules, the plural form of most nouns is to add S at the end of the word. As a singular form of countable nouns, yo-yo also follows this rule. Therefore, when it is necessary to represent multiple yo-yos, just add S to the singular form to get the plural form. For example, if we have two yo-yos, we can say two yo-yos.