"Good evening, thank you."
Translation:Dobrý večer, děkuji.
You need to learn the declension table for the word dobrý. You can find it in https://en.m.wiktionary.org/wiki/dobrý#Declension
dobrý is nominative masculine singular case, among others. Dobré is nominative neuter singular case, among others. Dobrou is instrumental feminine singular case, among others. Too numerous to list here.
I believe you are talking about declension. In the singular form and the first grammatical case (nominative), there are three gendered 'versions' of the word.
Masculine: "dobrý" -ý Feminine: "dobrá" -á Neuter: "dobré" -é
Note that the gender always refers to the grammatical genred of the noun the adjective refers to, which may be unrelated to the actual gender of the object.