The word "simply" means doing something in an easy or straightforward way. It is used in its basic form, so there is no need to change it for present simple.
Here is a sentence using "simply" in present simple: "She simply tells the truth."

The word "open" means to move something so that it is not closed, like a door or a book, and you can see or use what is inside. In present simple, the word remains "open."
Example sentence: I open the window every morning to let in fresh air.