In general, when you say "control plan," most of us think of the AIAG (automotive) type, which is probably not what you're looking for. If I'm correct, there is probably no standard format for it and it's probably best to build something of your own because requirements differ from company to company.
You can start by doing a simple flow diagram of the process, and then listing the control requirements for each step. You can decide for yourself whether a graphical format is enough, or whether more detailed documentation is appropriate. It's also a good opportunity (before doing the control plan) to do
PFMEA (Process Failure Mode & Effects Analysis) which is the process of examining each step in the process for potential failures and taking measures to prevent them from happening.