your friend need to have another bank credit card in order to balance transfer to other bank.. find those bank which offer lowest or near to 0% fees BT, apply their card and submit the balance transfer to that bank..
the problem now is whether your friend new credit card application in that another bank will get approve or not...if too much late payment or miss payment record in ccris records, bank will reject any new cc/loan application..

if he cannot pay in full, each month, then he SHOULD STOP using the card and continue clearing the oustanding.

chances to apply new card is low to no chance to get approved considering the bad records.

sorry to say, forget about spending more with the card or applying new cards. dont keep digging the debt hole deeper.

1) does he have other cards to BT to?

2) if no, have to apply. chances to get approved is slim.

3) if yes, does the card/bank have 0% BT? study each card/bank. if no 0%, is the upfront fee % rate worth it?

Try PBB or AEON for 0% BT but good luck with the application.

To be honest, the very important key is - how much is your friend earning per annum, whether he can apply for new cards to do BT etc depends on that.
Since your friend did not miss any payment, should not fall into bad credit score that much.
For example, some of us here have so much balance in credit card account (due to BT) but with prompt payments and adequate income, there's no problem applying for new cards.
Anyhow no harm trying since not much damage compare to currrnt situation.
So, good choice for BT would be 0% ambank, pbb, aeon. But application is super strict and stingy credit limit
Now ambank also have 0% bt for 1 year. Which may suit your friend. Ambank have generous CL, hopefully easier to get approval too.
So i suggest your friend to try ambank first.
Note: applying too many will kind of leave an 'enquiry' to the credit report. So i suggest to prioritize your friend's application to the banks that are easier to get, ie in my opinion ambank > aeon > pbb.
In fact i would not try aeon & pbb if ambank fails. Might scout for other banks first even though may not have 0% bt.