Spray the stains with a cheap aerosol hairspray, then re-launder. You can also try using a laundry pre-treat. Don’t dry the clothes in the dryer again until the stains are gone or will not lighten any more.
If the dress does not need to be dry cleaned you should just be able to remove the marks by spraying with a laundry pre-treat and laundering as usual. If it needs to be dry cleaned make sure they are aware of the marks when you leave the dress with them.
Use Citrus Gel Spotter. Apply it to a clean white cloth and work it through the gum, then rinse the jacket to remove the Citrus Gel Spotter. If the jacket requires dry-cleaning, make sure the cleaners are aware of the gum when you leave it with them.