I see a lot of information in the opposite direction: if you have a PS4 linked epic account you can't use it on Switch. However I'm wondering if you played on Switch first can you then play on PS4?
I tried it and the answer is no, you cannot log in to your epic account on PS4 if you've used it on the Nintendo Switch
yes, you can link your accounts. In order to do that, you have to go to epicgames.com with a PC*, sign in, go to "account", then "CONNECTED ACCOUNTS", and then link it from there.NOTE: there is a small possibility that you will lose your progress, so I suggest that you link it with a test account first