What is the indirect object pronoun, adding it to the infinitve, in the place of the parentheses, andrés no quiere darlo (a ella)

A direct object pronoun is the noun that the action is being done to. If I say "Andres threw the ball" then the ball would be the direct object pronoun.

A indirect object pronoun is something that is being affected by the action done to the direct pronoun. So if I say "Andres threw the ball to Anna" what is the indirect object pronoun? Its Anna.

So the sentence  that you are using is translated to Andres did not want to give it to her. (Andrés no quiere darlo (a ella)) This is already grammitically incorrect. The correct way (for new people to the language) to say this would be:

Andres no quiere le (Indirect) la (Direct) da. (if you are extremely new to spanish this would pass you off and it would be fine)

But if you want to be even more grammatically correct you would use:

Andres no quiere se la da. (I suggest you use this;both sentances mean the same thing, but in spanish you usuall y dont do double L's when using indirect and direct object pronouns)