Thrown lids are trimmed while seated on their corresponding jar. In essence, the jar itself becomes a trimming chuck. Trimming the lid is the same process as trimming out a foot ring. The only substantial difference is in what areas are removed. You may, however, find it somewhat easier if you keep a fingertip on the top of the lid. This will help it not to shift in the jar's mouth.
If you are trimming out a handle, make certain that you do not encroach into the handle's area with the trimming tool too soon. Remove the outer excess clay first. Remember that the lid's thickness should match that of the jar's wall.
When trimming out handles, a variety of loop and ribbon tools with slightly different profiles may be useful. These allow you to undercut the handle more easily and shape it to the desired configuration.
Once the lid (and possibly the foot of the jar) are trimmed, return them to a shelf, with the lid in place, to continue drying. Still keep paper toweling across the gallery to separate the lid and jar.