Easy, plug the balance cable either directly into your charger (if it has a set of balance ports) or into the relevant port in your balance board (that came with the charger). Then buy a JR charge cable.
Give us a minute and i'll find you a link in the UK.
Couldn't find UK. But this is what you want.
https://www.the-border.com/YUKI-Y600032.html
And you should have got something like this with your charger
https://www.the-border.com/SkyRC-Mul...600056-01.html
I have about 6 of them. None have ever been used!