How do I convince my wife to leave my three month old baby girl with me alone. She is afraid I won’t be able to handle it?

When your wife is around in the house, try to learn as much as possible from her, diaper changing, milk feeding, bathing and etc. With her presence, try to practice in front of her with the baby. I believe if you are feeling confident in handling baby, your wife will sense it too. You can start with taking care of baby alone for short hours first instead of whole day.