I understand that Yum's blacklist is for the purpose of keeping a record of employees who are detrimental to the company's interests, and who have a certain status or length of service. If your departure is not related to this, no need to worry. Although the trainee assistant may not leave much trace in the group file, it is still recommended that you should take the initiative to mention your previous experience in Pizza Hut. The examiner will definitely ask about the reason for your previous departure, and you should think of a statement in advance, not to say that it is because of some people's problems because the examiner will think that you do not have a good sense of teamwork, which is very important in a foreign company, and you can find some emergencies to be used as an excuse, after all KFC and Pizza Hut are managed separately, and the examiners won't go to your former workplace to deliberately ask for proof for an ordinary employee - assuming, of course, that there are no other problems with your resignation from Pizza Hut. Good luck.