Hi all, thank you for all of the responses. I am currently abroad and it's difficult for me to contact my friend and to reply here, so thanks for your patience.
If you currently still face this problem, probably the "sent" amount is already back to your friend's wallet since that transaction probably dropped by the network already. It only shows "unconfirmed" because of the electrum's server your friend is using.
You can request to send it back to you either using RBF by sending another transaction by with higher fee (5sat/vb =$.04 as of writing).
You can also request to change his/er electrum's server so the amount will show to the wallet and send it back using desktop and android wallet of electrum
And lastly, import to another wallet using unstoppable and mycelium if using android, although this is optional and note it may risk your friend's word seed due using another wallet if not used properly.