Conditional should and modal should have different patterns in English.
Modal should follows the typical S-V-O sentence pattern:
subject + modal + base verb
The meaning of modal should is a suggestion.
You should pay attention in class. (I suggest that you pay attention in class.)
Conditional should has inversion in the sentence, which means that the subject and verb are switched.
The pattern of a conditional should sentence is:
modal + subject + base verb
Conditional should means if and is used for hypothetical situations.
Should you need anything else, please call this number. (If you need anything else, please call this number.)