How to Append a list Into Existing JSON File

Question

HI all,

Existing JSon File Contains and File Saved as UniqueID.JSON

{

UniqueID :1123,

Datetime:"",

User:"",

}

And  I need to read the file and append  the courses (It's List) taken by the user  into Existing Json File.Please help me 

Expected output

{

UniqueID :1123,

Datetime:"",

User:"",

Courses:[

{

name : English

},

{

name : Maths

},

]

}