Questions that face anyone who models processes in BPMN: to what level should the process be decomposed? Is it worth to depict how the task is performed?
Although there may be exceptions (see below), it's generally not worthy because results in overcomplicated diagrams. Detailed instructions are valuable indeed but usually it's better to place them to the task description instead. Add step-by-step instructions, checklists, references to the operations manual etc. Focus on the coordination of tasks performed by different roles on the diagram level.
Advanced BPMN modeling tools let user add description to a task and publish diagram accompanied by descriptions and other attributes as a document and/or hypertext. As an example, here is how it looks in Bizagi Modeler (source file):
It may make sence to depict the task logic if it's non-linear, e.g. if it contains gateways:
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