How to update IndexedDB

Hi experts, I want to update my IndexedDb that the value of msales be updated and be added to 30.00 to become 250.00 in result and the value of created will remain.

My IndexdDB
key = 1975 value = {msales: "220.00", created: "11-18-2019"}

Js

function gsaleslocal(){
	var sales = "30.00"

	var transaction = db.transaction(["gsales"],"readwrite");
	var store = transaction.objectStore("gsales");

	var mytrx = {
	    msales: sales,
	};

	var request = store.put(mytrx,1975);
	
	request.onerror = function(e) {
			console.log("Error", e.target.error.name);
	}
	request.onsuccess = function(e) {
			console.log("Successfully added");
	}
};

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