So I know how you feel as I took French and Spanish at GCSE but I know that you will definitely have it harder as the new GCSEs are absolutely brutal, I took the new English and maths exams and that was enough! But having said that I did get A*s in both languages and in my French gcse as a whole I got 100% so I feel I can probably offer some help at least. The main thing that I learnt from my speaking exams was that it’s not so much what you say but how you say it. You need to make sure that you sound confident because that will instantly show the examiner that you know what you’re talking about even if the words you’re saying aren’t hugely impressive. Also make sure your pronunciation is good, that is the most impressive thing for the examiner. Most people taking languages quite honestly have very poor accents so if you master a good accent that’ll instantly boost your grade. Another thing I found was that it doesn’t hurt to throw some humour in there. I’m not saying you should turn into some German speaking version of Russel Howard or anything but tell a funny story or something. Like in my French when I was asked if my family eat in restaurant often I said yes and then told the examiner about the time we were in France and because my brother is so bad at French he ended up ordering a pot of ice instead of ice cream. I know that’s not really funny but my middle aged examiner seemed to find that hilarious.
Basically you just need to be confident and make sure if you’re nervous it doesn’t come across that way. Regarding preparation this is gonna sound weird but I listened to French and Spanish songs and tried to understand what they were saying. My thinking behind it was if I could understand what singing people were saying then they wouldn’t ask me anything I didn’t understand. This also helped with my listening exams too.
I hope this helped