What to do with it, and when

Give it a few days before doing anything strategic. Decisions made on day one are made by somebody who has just lost something, and they tend toward either abandoning the goal entirely or firing off replacements without thinking about them.

Then, once it has cooled, do two concrete things: ask for feedback if it is available, and look honestly at whether anything was actually within your control. Most rejections contain one fixable thing and a great deal that was never yours to affect. Separating those two is the whole exercise.