السلام عليكم
The video above shows a teacher from the Middle East explain to her class how the impact of reciting Istighfār can help a person.
The video shows the teacher pour Coke/Pepsi in a clear glass whilst saying out load different sins and bad behaviour. This is an attempt to show how sins can make the heart go black as depicted by the Coke/Pepsi.
The teacher then asks the students what can be done to help clear the glass of the Coke/Pespsi i.e sins and they shout out Istighfār.
As the students say Astaghfirullāh repeatedly the teachers pours water inside the glass to show how repeated Istighfār can clear the glass from Black liquid (Coke/Pepsi) to clear liquid.