The 19-year-old Blues defender will remain at York Street for a third and final month.
"Asa is a young lad with a huge amount of talent, who is enjoying his time with us while he continues learning," Pilgrims boss Steve Evans told his club's official website.
"He has spoken highly to the management team at Birmingham City of the way he has been treated and of the coaching that he believes is making him a better all-round player.
"He was delighted when I asked him if he would stay with us for a further period and I thank Steve Bruce for sanctioning the request."