I say, and with God's help: Wudu (ablution) is valid if water does not enter the mouth; because rinsing the mouth is a Sunnah of Wudu, and it is not obligatory. You should bring water into your mouth; because the water that remains in your mouth after rinsing is excused and does not harm your fasting, so that you do not miss the reward of the Sunnah. And God knows best.