The engine uses spacer shims the ride on top of the spring buckets to adjust the valve clearance.
These require some skill to remove and replace even if you have the tools. The tools can be purchased aftermarket. The shims are a Toyota dealer part.
The valve clearance is measured engine cold. If adjustment is required a chart is referenced having shim thickness on one axes and measured valve clearance on the other to find the replacement shim.
I don't remember what a shop would charge but a complete adjustment of all valves was not cheap.
If it is a valve in the back cylinder head getting the valve cover off is also time consuming.
If just one valve you could most likely make your own tools, you will not know the shim thickness until you have it out. Thus keep this in mind.
The chart is available online if you look around or the dealer may be able to determine it.