I’ll take this one.
FYI: This article is talking about some particles. Particle を is used to attach with an object. “To take this one” is a combination of a transitive verb and an object. I guess some of you now wonder why the Japanese sentence doesn’t use を instead of に.
これをするよ。(casual) ==> 私はこれをします。(formal) = I will do this.
これにするよ。(casual) ==> 私はこれにします。(formal) = I will pick this up among other choices.
You cannot replace を with に in this case.
As the abovementioned article explains, に is often used to show a destination (= to/toward). これにするよ sounds to me as a Japanese native speaker like “there are several ways to choose, but I finally picked up the right one”. Your mental journey ended in choosing the right destination. So, we use に in this context.