How to join new sweet branches to my old sour grape branches?

[Shaba]

I have got a grape vine in m,y garden and have been growing for the past 4 years. It has grown very well and big but has always been our. I let it ripe as much as I can but it is still sour.

I was told by someone that I can buy sweet grape branches and attach it tot he sour one.

Have you heard of this method? if so does anyone know where I can get someone or buy it.

My number: xxxxxxxxxxxxxx(croydon)

thank you,
shaba