Unfortunately if the glasses are part of the source picture, it is impossible to stop all movement of the glasses. However you can try to reduce this by sacrificing some eye movement.

If you are using Auto Motion for your character, try going into "Auto Motion Settings" from the top toolbar and reduce the amount of movement of the eyes themselves. This will help.

If you are creating your own expressions using the puppet editor, then just reduce the number of blinks you add to the minimum and don't record any excessive movements of the eyes.