If it was originally packed with glue, just stick it with 502 or super glue (you can buy it in supermarkets around 2 yuan).

You can go to the clothing DIY store to buy new fixing buttons and glue sticks. First, bake the glue stick soft with a lighter, then quickly stick the melted glue behind the brooch before the glue stick cools, and then put the fixing buckle on the glue and let it cool.