I don't know Rishi (my guess is that Rishi's are agniras and Atharvana/Bhrigu) or gods of the following verse of 11th hymn and 3rd kanda of Atharvana Veda
यदि क्षितायुर्यदि वा परेतो यदि मृत्योरन्तिकं नीतएव | तमा हरामि निर्ऋतेरुपस्थदश्पार्शमेनम् शतशारदाय ||
अ०वे० काण्ड-३ सुक्त-११ मन्त्र-२
Be his days ended, be he now departed, be he brought very near to death already, Out of Destruction's lap again I bring him, save him for life to last a hundred autumns.
Atharvana Veda kanda-3 sukta-11 mantra-2
Here the mantra says be 'his', now 'his' is clear from the notion of reader or the one who is astika and follows vedic order.
Since every veda mantra has a god and a rishi , the word 'I' can refer to that god , If no then it must refer to bramhan as he is all powerful and god of gods. So who is the 'I'.
Disclaimer -: Atharva Veda mantras cannot be recited without consultation with a learned man(in vedas)/It should be recited by a learned man. If recited without consultation they produce no or opposite effects.