Edit and replace long text in a single cell

Hy all

i attached some file

in this file, ther's old text and new text coloumn which contain long text in a cell

to make it clear, i attach a picture
Untitled.jpg

how to replace a specific text:
1. the name XXX with cell B3
2. username with with cell C3
3. password with cell D3

the output is just like New text

thankyou so much for the help