Hello & welcome,
Brown lump after extraction of the tooth is nothing but the indication of proper healing of the socket & needs no special treatment unless got infected secondarily.
Even you have not mentioned any more symptoms related to it which shows absence of pain & discomfort.
But as the tooth was infected before extraction, you will have to take care of the extraction socket by proper cleaning. Gargling after taking meals or after brushing is proper way to avoid any food lodgement in the extraction socket & you are already doing that.
If you get any pain or swelling there in the same location ,you can visit your dentist
for clinical examination.