automatically editing many .tec files

Hi there,
I've many .tec files that been created after mistakly deleting photos on my android.
I'm trying to edit them, by deleting the 6 first chrs. and the last one.
Then, I'm changing the file from .tec to .jpg.
I have 3000 files!!!
Is there any way to make it automatically, like a script or cmd commands?
Thanks for your kind help/
Asaf

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