If Donald Trump would have been killed,how would a new candidate have been picked?

In the recent assassination attempt against Donald Trump,the former President was wounded ,but thankfully,not seriously injured.A bullet hit his ear,but if the assassins aim would have been better,that bullet might have gone through his head!If ,God forbid,he would have been killed,what is the exact process through which a new candidate would have been selected?Please give only serious answers:anything mocking Trump or any "Trump is Hitler"rhetoric will be promptly deleted.