If you have a lot of recipe materials, you can combine 5 cards at will, use one card to strengthen 1 star to 1 star, and use another card to strengthen 1 star to 2 stars.

Use one more card to strengthen it to 1 star, and then use these two to strengthen the 3-star card to 4.

If there are not many, just use the secret to combine them into one. A 3-star card, combined with a 1-star card, becomes even stronger.

Or just get the best and get 4 stars