Hello, parrot Dera

Parrot Dera, honestly, it's been three days since I bought him from someone and found him sick. I swear I don't know how to handle bird diseases. I took him to a veterinarian who said it might be a respiratory infection and gave me some medications, but I don't know how to handle him. To be honest, when I bought him, I asked the owner, and he said the reason for selling is that he has other birds and doesn't want him, but he didn't mention any health problems. Besides that, he bites anyone who fears God and knows him, and behaves well. 250