how to clean calabaza made of pumpkin
You cannot really clean it the way you would clean a porcelain cup.
If what you see is only tea buildup, then you don't have to worry about it. It is normal that it takes on some tea smell and discoloration. Because you continue making the same tea in it, there is no problem about that. Also, if you have mineral buildup (limescale), there isn't much you can do about it, maybe try scratching it off.
In case you have mold, there is again nothing you can do, since it has colonized the whole body of the gourd. Then there is no way to clean it, you will have to throw it away. To prevent mold in a new gourd, make sure it is always well drained after cleaning, and don' store it in a place with high humidity. If you have a persistent mold problem, try storing it with a rice sachet, or a silica gel sachet.