Make sure that the water is deep enough to completely submerge your jar on its side. If you are removing the label from multiple jars, make sure that the water is deep enough to completely submerge the largest jar. Let water get inside the jar so that it weighs it down. You don't have to wait exactly 30 minutes, but you have to wait long enough for the water to soak the label and dissolve the glue.

How would you rephrase that briefly using Indonesian?
Isikan air hangat ke dalam bak cuci piring. Buka stoples, masukkan ke dalam air, dan tunggulah selama sekitar 30 menit.