L10s. I received cleaning solution-how do I get it into container

The solution is in a huge bottle. The container that goes in between the two tanks has two small openings. The one that lets the solution out and one more. The last one has a cover but  the cover doesn’t want to come off. Do I force it off and put the solution in that opening?  Please show a picture if possible.

Here is a video showing how to add the solution

https://youtu.be/m6rqHyhyHjs?is=tlkUbeBXVwsxgesr