Would someone please help me to understand the following sentence?

Hello,I'm now suffering from the following sentence;"They can find realistic plans should they need to be implemented or can find a necessary reaction.”If the sentence is as follows(replace “should they” with “which”);"They can find realistic plans which need to be implemented or can find a necessary reaction.”I can understand it.But I can’t understand what the words “should they” mean."should” is auxiliary verb and almost the same meaning as “need”, which is also in this phase.Would someone please explain me how I can interpret this sentence?