A variety of tools can be used to move frit and powders about to get the shape and edges you want.
One simple tool is a brush. It seems that a soft water colour brush is suitable for very delicate manoeuvring. There are various shapes and sizes for more and less delicate shaping. A stiffer hogs hair brush will move greater volumes.
You can also use a brush to pick up stray pieces of frit. Get the brush damp and touch it to the grains of frit to pick them up. If you do not have excess water on the brush, you will leave no mark behind.
Colour shapers with shaped, rubber tips are good for stroking and pushing frit and powder into place. There are a variety of tip shapes for various uses. Wooden tools as used for shaping clay can be useful in the same way, although they are not flexible.
Another tool that can be used is an adapted keyboard vacuum.