In JS which object property is use when we want to add new value but we don’t want to change it’s previous value

I WANT TO add new values in an object but I don’t want to change the previous values.

I tried freeze method but it is not solution for this problem then I tried seal methods it also don’t work, then I searched on chatgpt, it says to me use const but that is not a solution then I searched on google it shows the stackeoverflow link, so please kindly make me understandhow we can add new values without changing its previous value?