Below some tips and links on how you can prepare for PST.
1. Practice it. You can find some guidance on PrepLounge: https://www.preplounge.com/en/bootcamp.php/interview-first-aid/master-the-problem-solving-test/guide-to-improving-speed-in-written-tests-such-as-the-pst
McKinsey PST is the hardest one, so I recommend starting and tracking your prep using PST materials. If you have good results with PST, other tests are not a problem. For this you can:
• Buy Viktor Cheng test prep program - the best materials I've seen so far.
• Practice your math. It is very important.
Do the 2nd test and check the score
Also, you can find a good number of PST tests online.