From a quick image search, I think this one has the sliding button for the shaft lock. Don't forget to unplug it first and pull the bit out a bit (1/8" or so) before tightening because bottomed out bits can cause some chucks to not tighten properly. I assume that type of shaft lock would interrupt the power but obviously you would have to unlock the shaft before operation.
Many chucks work like this: Unplug, lock the shaft (wrench, lever, button or whatever), loosen the chuck until it gets easy to turn. If the bit isn't loose at this point you keep turning the nut and you'll feel it get stiffer to turn again. Then the turns will loosen the chuck internally and release the bit.
Important: Never tighten a chuck without a bit (this can damage the collet (collets for many older routers are hard to find). Never run a router with a loose chuck. Routers run at very high speeds ( ~20,000 RPM ). If a bit comes out it can be very dangerous - ricocheting around. A previous member needed surgery to repair his ear.
If you can't find your exact manual, try to find one that looks like it. Often very similar routers (with different numbers) were released with maybe different horsepower or improvements etc. The operation would likely be identical but a few parts might not be. Try this one to see if it's similar in operation.
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