Symptoms: Car won't rev, slow above 4k RPM

Knowns: Dealer says the IMRCs don't open

Question: How do I test this? Should I attempt to manually actuate them with a tool somehow? Is the broken cable visually obvious or do I have to disassemble it to figure it out?

Car is a daily driver, anything I need to have 'on hand' to reassemble or ensure that its not down for days waiting for parts?

Thanks
Scott