The simple present is commonly used in preference to the auxiliary “will” in conditional clause.
However, “will” and “won't” occur in adverbial clauses, particularly in “if-clauses”, in certain uses. In general, the difference between the simple present and the modal is that the simple present refers to an assumed future actual situation whereas the modal refers to the assumed predictability of a situation or of situations. More specifically, will and won't are commonly used:
(1) where the modals have a volitional meaning:
If you'll help us, we can finish early. ['are willing to']
(2) where the modals express timeless and habitual prediction:
If drugs will cure him, this drug should do the job.
(3) where the modals express the present predictability of the occurrence
or nonoccurrence of a future situation:
If the water will rise above this level, then we must warn everybody in
the neighbourhood. ['If the water is going to rise above this level, then
we must now plan to warn everybody in the neighbourhood']
A Comprehensive Grammar of the English Language By Quirk, et al. p.1008
Student or Learner