"Otherwise" is a conjunctive adverb, so an additional coordinating conjunction ("and", "or") is not needed. Replace the coordinating conjunction with a semicolon.

If X, I do Y; otherwise, I do Z.

"Otherwise" is a conjunctive adverb, so an additional coordinating conjunction ("and", "or") is not needed. Replace the coordinating conjunction with a semicolon.

If X, I do Y; otherwise, I do Z.

You can also use two separate sentences.

If X, I do Y. Otherwise, I do Z.