By definition, a gerund is a verb that ends with -ing.
With this in mind, we can see that "dancing" and "writing" are gerunds. If we need to change them into infinitives, then we need to know what infinitives are.
An infinitive is the basic for of a verb with the word "to" in front of it. If you look at the end of your sentence where you have "to paint," you have an example of an infinitive.
To change our two gerunds, we need to drop the -ing and make each for basic: "dance" and "write". Then, we just need to add the word "to" in front of it, making it "to dance" and "to write."
Thus, our sentence should now read "I keep telling people that I love to dance, to write, and to paint.
