I would like to reduce the number of instruments as I have 29 groups but xtabond2 produces 359 instruments. I understand that number of instruments has to be less than the number of groups.
Can some one tell me how to do that using the command below?

xtabond2 L(0/1).gr inf inv govexp op popgr atm, gmm(gr, lag(2 .)) gmm(inf inv, lag(1 .)) iv(govexp op popgr atm, eq(diff)) h(2) robust