How can I replace the first value in the second list with the last value in the previous list?

In this list of objects we have value groupID, Which contains a list.

What I want is to replace the first value in the list with the last value in the previous list.

let testArr = [
    {groupID: [1900, 1890, 1880], Letter: "A"},
    {groupID:[1888, 1898, 1908, 1918, 1928, 1938], Letter: "B"},
    {groupID: [1927, 1917, 1907], Letter: "A"},
    {groupID: [1912, 1922, 1932, 1942, 2012, 2022, 2032, 2042], Letter: "B"},
    {groupID: [2039, 2029, 2019, 2009], Letter: "A"},
    {groupID: [2013, 2023, 2033], Letter: "B"},
]

The result is:

let testArr = [
    {groupID: [1900, 1890, 1880], Letter: "A"},
    {groupID:[1880, 1898, 1908, 1918, 1928, 1938], Letter: "B"},
    {groupID: [1938, 1917, 1907], Letter: "A"},
    {groupID: [1907, 1922, 1932, 1942, 2012, 2022, 2032, 2042], Letter: "B"},
    {groupID: [2042, 2029, 2019, 2009], Letter: "A"},
    {groupID: [2009, 2023, 2033], Letter: "B"},
]

I have this code, but it’s silly and doesn’t work with async and await:

let add = []

for (let i = 0; i < testArr.length; i++){
    if (testArr[i].groupID.length != 0){
        add.push(testArr[i].groupID[testArr[i].groupID.length-1])
    }
}
for (let i = 1; i < testArr.length; i++){

    testArr[i].groupID.splice(0,1, add[i-1])
}

and Thanks in advance.