Reference book recommendation
There are a series of reference books on the market that sell the third-level certificate of psychological counseling, which seems to be called "National Vocational Qualification Training Course-Psychological Counselor Level 3". There are textbooks, exercises and answers. I suggest you buy this, which is more symptomatic.
Psychology textbook recommendation
General psychology can be seen in Peng Yongling's edition; Developmental psychology can be seen in Lin Chongde edition; Psychometrics can be seen in Dai Haiqi's edition; Social psychology can be seen in the Hou Yubo edition. You don't know much about the textbooks of psychological counseling and abnormal psychology, but you should study psychological counseling seriously, especially some therapies, because the third level mainly tests these, such as rational emotional therapy and behavioral therapy, and you should read more diagnostic cases.
Learning time planning
Because you are self-taught, it may take some time. It is estimated that you can finish at most two courses a week, not including solving problems. I think it will take a month at the earliest
Examination training class
There are also many training courses for this kind of exam. You can consider applying for it, which will make you learn faster, but you should also be cautious and find a real psychology teacher.