If I am in my 2nd rakat, I finished to recite the tashahud and then by error, I start to say ‘Assalam’ , the zikr of salam
And then I correct my error by reciting the zikr of tashahud again.

Do I have to do sajda e sahw for the zikr of salam that I said?

Or I have to repeat namaz again?

As soon as you realise, you can continue your Namaz by leaving the salaam (no need to repeat the tashhahud) then doing Sajdah sahw at the end.