Adjusting the engine valve clearances is adjusting the valve lash.
Honda does not recommend "flushing" the transmission fluid.
If it's an automatic transmission you need to open the drain port and let as much fluid drain as possible, then refill it.
But that will only get about 1/3 of the fluid each time you do a drain-and-fill. So do the first drain-and-fill, drive it a few miles, then do a second drain-and-fill, drive it some more, and then do a third drain-and-fill.
If it's a manual transmission then just one drain and fill will take care of it.
Also if it's a manual you should replace the fluid in the master and slave cylinders for the clutch. The fluid is standard brake fluid.
And if you've never changed the brake fluid that needs to be done, too.