Question

"I didn't see you either"I said ( narration change)​

Answer 1

$\sf{\large {\underline {NARRATION}}}$ :

$\tt{\underline {In\: Indirect \:Narration}}$ : I said that I had not seen you either.

$\sf{\underline {RULE}}$ :

Did ( Simple Past )

$\implies{Had\:(\: Past \:Perfect\:)}$

Verb's 1st form

$\implies{Verb's \:3rd\:form}$.