the first option is grammatically incorrect, as you've already used did as auxillary so you cannot use past tense as watched again.

First one is wrong, second one is right :)

Thank you so much 🙏🏾

I didn't watchED TV is incorrect. It's Past simple and you cannot use ED ending in negative sentences. I watched TV last night. But I didn't watch TV last night. the structure of Past simple: Subject/noun+V+ed ending. But the negative structure is: Subject or noun + did not or didn't + V without ed ending