Where can I find ATC Guidelines for handling Airport Incidents?
I'll answer from US ATC perspective having worked ATC at 3 different airports. First, I'll describe the alerts, then I'll describe training

As with all things, each airport has different procedures for how they handle emergencies or accidents. For each airport, the airport operator and the ATC Tower will come up with numerous Letter's of Agreement for how they want to handle things from lighting to emergency services. My first airport had 2 alert conditions, Orange and Red. Orange was go to standby positions, something is inbound requesting emergency services to be ready in case something happens. These are relatively common. Red was an actual accident/crash.

The more common alerts are broken up into 3 categories I, II, and III. Alert I alerts are usually, a heads up to the crews to just be ready, but not go to the runway. Alert II are go to the standby positions, somebody's inbound with an issue and services are needing to go there. When this alert is declared, often as soon as the plane lands the runway is closed automatically until the airport inspects it(making sure no debris fell off the aircraft on landing). And Alert III is an actual crash. Most of the times, this is an immediate closure of the airport. This is due to the emergency services focusing on the accident and can't be available if something else were to happen on the field. Note, super large airports can have enough spare capacity to keep portions of the field still operating, depending on what all they have and how their command/control works.

Training wise, it's often just on the job training and usually the light emergencies, where people just need to get back or gear stuck or similar non-crash emergencies. Usually in the course of a controller's training at their facility they'll get a couple of these and know how to react. There are discussions of past issues as well, when there's time and resources available to do these types of discussions. Full on crashes, as stated are rare, so likely the first time a controller has to deal with it, they'll have seen small issues in the past to help prepare them.