As soon as you notice the gum on the leather, use your fingers to gently pull as much of the gum off as you can. Ensure that you don't spread the gum over the leather as you're pulling. Take a piece of clear tape and lay it over the gum. Press on the gum so it sticks to the tape. Pull the tape off and some of the gum should come off with it. Keep laying fresh pieces of tape and lifting the gum until all of the gum is removed. You may go through a whole roll of tape depending on how strong the tape is. The leather might be dirty once you've removed the gum. To clean the leather, you can use a commercial leather cleaning product or use a mild dish soap and warm water. Just wet a sponge in soapy water and gently rub it over the leather. Avoid pulling or scrubbing on the leather. You may be able to wash away any tiny bits of gum that are still stuck to the leather. Dip a clean cloth into a little dish of mineral spirits. Slowly wipe the cloth over the sticky area on the leather. Once you've removed the sticky residue, use a clean, dry cloth to wipe over the area. This should thoroughly clean the leather and remove the last of the gum.  Mineral spirits are also called white spirit and mineral turpentine. Use the mineral spirits in a well ventilated area and avoid touching the soaked cloth with your bare hands since mineral spirits can irritate your skin. Don't throw away the cloth that you dipped in mineral spirits. Instead, place it in a container with water and take it to a local hazardous waste facility. Use the manufacturer's instructions for protecting the leather or use a commercial leather conditioner. This will moisturize the leather since you've probably stripped away some of the protective oils in the fabric.

TL;DR in Indonesian:
Lepaskan permen karet sebanyak-banyaknya. Lepaskan permen karet menggunakan selotip. Cucilah area tersebut dengan air sabun atau produk pembersih. Hilangkan residu yang lengket menggunakan mineral terpentin. Oleskan kondisioner pada kulit.