Good luck everyone. Don't worry about how much you know. They're looking for potential for the undergraduate course, not the finished article or even the half finished article. We find out on placement how little we actually know even when we've graduated. Until you see things day in day out it's almost impossible to appreciate fully what the role of an SLT is.
All that said, though, the key qualities they're looking for match closely the competencies they expect to see in a fully qualified SLT. And there are plenty of ways to demonstrate those.
Have a look at band five person specifications if you like and try to think of examples where you've done something that demonstrates that quality or skill. That's as good a way as any to prepare for the interviews. Particularly where they run multiple mini interviews each question is targeting a specific thing from those competencies. So make sure you can think of specific and discrete examples for each. Best way you can prepare.
But don't try to sell yourself as knowing it all. I tell my past version of me: you know nothing! Because I really didn't. I knew just enough to know that it interested me and had just enough life experiences to know that I would probably manage certain aspects of the job and the course okay. And that was enough.
Don't underestimate it, definitely, and do try to reflect on how language and swallowing difficulties affect people's lives. Food and conversation are two of the things that make life most enjoyable. It can't be too hard to realise how your quality of life would be diminished if you lost or never had one or both! If it is hard, you're probably applying for the wrong course!