How do people pick themselves up for a rejected TC especially being an internal candidate?
This happened to me and I did find it difficult. I'm sure you put a lot of work into both your job and your application so I know it can feel like a kick in the stomach! I would take some time to focus on something other than the thought of a TC, like a holiday etc - its can be a lot to go through mentally so some time for yourself can really help.
Once you've had a bit of a break, I would write down all the great things you achieved as an internal candidate to remind yourself that you are a fantastic candidate, and be specific - firms that you apply for in future will see this and it will boost your application. Make a few notes on the feedback you received and how you can work on it - I would recommend speaking to your supervisor to get their thoughts too. I would also start to pull together a list of firms that you can aim to apply for this year to give yourself a new focus, especially as its almost the start of the new cycle so its a perfect time for a fresh start.
Also - are you able to re-apply to the firm you are currently at? If you have the option but you don't feel like it right now, I would take some time to consider and speak to your supervisor, because in re-applying in the next cycle you can apply what you learnt from this time round and have a stronger chance.
It can feel like a punch to the gut being rejected as an internal candidate but remember its not personal and so often comes down to a numbers game - if you're already working for them then you are definitely worthy of getting a TC with a great firm wherever that may be.