You should be sure of what you intend to accomplish. Has your default been entered, or has a default judgment been given in favor of the other Plaintiff. Those are different. Entering default is the first step in obtaining a default judgment. The motion that you will bring depends what relief the court has granted to the plaintiff.

There is no substantive difference between "setting aside" and "vacating" any judgment, including one obtained by default. However, there is a difference between a default, and a default judgment, and both would need to be set aside, or vacated, in order to undo the final default. Generally, a "default" is entered by the court clerk, at the request of the complainant, when a defendant does not respond to the complaint. Then, once the clerk enters the default, the complainant has to seek a judgment by default, and depending on the court and the circumstances, can be done by the clerk or by a judge. The default judgment, after a showing of evidence, is entered in the record, and details any monetary award, etc. If the defendant then wants to appear and defend after default and a default judgment are both entered, he/she will have to get both set aside/vacated, in order to enter an appearance and defend on the merits.

You actually need to do both. A default prevents the defendant from answering, but just setting aside the default would just mean that the plaintiff could request entry of default judgment again. Therefore, a defendant must both set aside the default and vacate the default judgment.

https://www.avvo.com/legal-guides/ugc/deadline-for-setting-aside-default-and-vacating-default-judgment-in-california?ref=kb_serp_title_3