If you will set your mind to a goal, you will eventually achieve it.

The appropriate phrase to replace the phrase in bold to make the sentence grammatically correct is “set your mind”

It is to be noted that this sentence is an example of First Conditional Sentences. In the case of First Conditional Sentences, we use the simple present tense in the if-clause and simple future tense in the main clause—that is, the clause that expresses the likely outcome. This is how we indicate that under a certain condition (as expressed in the if-clause), a specific result will likely happen in the future. Hence, considering the given option 3 becomes the most suitable answer choice.