If you are not satisfied with your PTE core test score, you can retake the exam after 5 days from the date your results get published. You will be eligible to retake the PTE core test only after the results of your previous exam have been published.
There are no limits on the maximum number of times you can take the PTE core test, and you can appear for the test as many times as you like. However, you can only register for one exam at a time, and to reappear for the next exam, you have to wait for the results of the previous one.