Hand washing is best but use gentle cycles if you machine wash. Use cool water and gentle detergent. When possible wash sequins inside-out.
Air-dry. Avoid using a dryer.
Sequins may melt or become damaged in heat so always air-dry.
Never iron. Damage to the sequins is too easy with an iron even with pressing cloth. Steaming with a wand held away or in a steamy bathroom is more appropriate if you must get wrinkles out.