There is a generic entry in the Tracker for "Tossed Salad" which lists 1.5 cups at around 33 calories. This would be a good guesstimate, if your salad contained assorted types of lettuce/ spinach leaves, cucumbers, peppers, tomatoes, onion, etc. Typical salad vegetables. It's the add-on's that add the calories. Bacon bits, croutons, cheese, dressing, nuts and seeds, etc.
So you could guesstimate how many cups' worth of each individual thing you took. Or use the generic "Tossed Salad" and then just guesstimate how much of the higher calorie stuff you took.