A little script to clear all your history at https://myactivity.google.com/myactivity

clear-google-my-activity.js

/**
 * A little script to clear all your history at https://myactivity.google.com/myactivity
 * 
 * Load Developer Console (usually F12), paste this into the Console and hit Enter (or Run).
 * 
 * Doesn't use any cool magic, just simulates clicking on all the delete buttons.
**/

var ClearGoogleMyAccount =
{
	numTimesRun: 0,
	numTimesToRun: 3,

	init: function()
	{ 
		ClearGoogleMyAccount.loadjQuery();
		// Give jQuery time to load, then get started
		setTimeout(function(){
			ClearGoogleMyAccount.queueClickDeleteButton();
		}, 1000)
	},

	loadjQuery: function ()
	{
		// Load jQuerry, because it was quicker for me to script
		var script = document.createElement("script");
		script.src = "//ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js";
		document.head.appendChild(script);
	},

	/**
	 * Clicks on all the Delete buttons which can be found - this causes a confirmation
	 * popup to appear
	*/
	clickDeleteButton: function () {
		console.log("Clicking Delete Buttons");
		jQuery('.swipe-div .fp-date-block-date-holder button').trigger('click');
	},

	/**
	 * Click on all the confirmation popups which can be found - this does the actual deleting
	 *
	**/
	clickDeleteConfirmationButtons: function () {
		console.log("Clicking Confirmation Buttons");
		jQuery('.fp-delete-confirmation-actions [aria-label=Delete]').trigger('click');
	},

	/**
	 * So that we can keep deleting until everything is gone, we use a function which
	 * can call itself.
	 **/
	queueClickDeleteButton: function ()
	{
		// Open up some dialog boxes
		ClearGoogleMyAccount.clickDeleteButton();
		console.log("Queueing clickDeleteConfirmationButtons in 1.5 seconds")
		setTimeout(function(){ 
			// Let the dialogs open, then click all the Confirmation buttons
			ClearGoogleMyAccount.clickDeleteConfirmationButtons()
		}, 2000)
		// See how many items we have left to delete
		var itemsRemaining = jQuery('.swipe-div .fp-date-block-date-holder button').length
		console.log(itemsRemaining + " Items Remaining");
		setTimeout(function(){ 
			if (itemsRemaining > 0) { 
				// If we have some items left, start deleting them
				ClearGoogleMyAccount.queueClickDeleteButton();
			} else {
				// To be sure we get everything, we run the script a few times. This accounts for Ajax loading/slow pages.
				ClearGoogleMyAccount.numTimesRun++;
				if (ClearGoogleMyAccount.numTimesRun < ClearGoogleMyAccount.numTimesToRun) {
					console.log("Running Clear My Google Account count: " + ClearGoogleMyAccount.numTimesRun);
					ClearGoogleMyAccount.queueClickDeleteButton();
				} else {
					console.log("Done!");
				}
			}
		}, 5000)
	}

}
ClearGoogleMyAccount.init();

Don`t work ((**

Hey Chupro,

Thanks for reporting the error - I've not used Google for a couple of years so I'm afraid I've not maintained this script and it's likely they've changed their UI since then.

I won't be updating this scrpit any more, but if you're able to you're welcome to fork it and fix the bugs.