Write a letter to your friend asking him for return book.
Dear Sarmin,
I hope you're doing well and feeling good, thanks to the blessings of God. I'm sorry I haven't written to you sooner. You see, I've been quite busy getting ready for my upcoming SSC exams. Honestly, studying has been taking up most of my time, so I haven't been able to think about you as much as I'd like to.
Anyway, there's something important I need to talk to you about. Do you remember that Practical English Grammar book by Thomson and Martinet that you borrowed from me last month? Well, I really need it back now. If it's possible for you, could you please send it back to me by mail? I would be incredibly grateful if you could do that.
That's about it for today. How's everything going on your end? Please give my warm regards to your parents.
Take care and talk to you soon.
Best regards,
Samia Rahman