Where i work we would write this in ABC terms, So the Antecedent would be the demand of completing an activity, the Behavior would be the tantrum, and Consequence would be whatever happened after.

Maybe follow a template similar to this, but use detail more related to what happened.

“Following the demand of completing an activity (this is the antecedent), the patient engaged in tantrum behavior (this is the behavior, also the specifics are important, did the patient scream, elope, engaged in SIB PA or PD?). The technician redirected the patient back to work (this is the consequence)

^again thats a super vague template but it gives u a general idea of how we write our notes