When the noun refers to an object (baño, comedor,etc.) it doesn’t changes gender, it stays the same.
The same happens when the noun has an e (inteligentE, jóvEn, etc.)
And when the noun ends with either A or O (guapA, altO, etc.) and you want to change its gender all you gotta do is swap them, for example: rubiO rubiA .
This applies for the 90% of words, hope it helps :)
