Hi!
First of all, congratulations on your TC offer!! 🥳 I was in a similar situation last cycle, so thought I'd share how I approached it.
I would politely email the graduate recruitment team of the firm that you are still waiting to hear from, and just explain that you have received a TC offer but still remain interested in them and wondered if they had any update on when you can expect to hear back - this is completely normal, and can sometimes speed up decisions (though not always). I did the same after receiving my TC offer, and the other firm were able to get back to me a day or so later. Even if they aren't able to get back to you immediately, they may be able to provide you with a rough timeframe in which you can expect to hear back, which is always useful!
Sometimes they might ask who the TC offer is with (as I was asked this), but this is usually just so they can see who they are competing with in relation to talent. If you have a deadline for accepting the TC offer, I would just mention this in the email as it might be useful for the firm you are waiting to hear from to be aware of this.
I hope that assists, and best of luck with your decision!