Tutorial: https://www.youtube.com/watch?v=hIqMrPTeGTc 
Paste the below code in your browser console (F12 > Console):
(()=>{
    markAllVideosAsNotBeingInteresting({
        iterations: 1
    });
})();
async function markAllVideosAsNotBeingInteresting({iterations}) {
    for(let i=0; i<iterations; i++) {
        await markCurrentVideosAsNotBeingInteresting();
        console.log(`Iteration ${i} completed. Waiting 300ms`);
        await sleep(300);
    }
   if(confirm("I'm done! Do you want to reload the page", "Yes")) {
    location.reload();
   }
}
async function markCurrentVideosAsNotBeingInteresting() {
    const videoMenuButtons = document.querySelectorAll("yt-icon.ytd-menu-renderer");
    for(let i=0; i<videoMenuButtons.length; i++) {
        if(!videoMenuButtons[i]) {
            continue
        }
        videoMenuButtons[i].scrollIntoView();
        await sleep(10);
        // Open the video menu
        videoMenuButtons[i].click();
        await sleep(50);
        // Click on "Not interested" button
        var notInterestedButton = document.querySelector("#items > ytd-menu-service-item-renderer:nth-child(5) > tp-yt-paper-item");
        if(!notInterestedButton) {
            continue
        }
        notInterestedButton.click();
        console.log("One video has been marked. Waiting 100ms");
        window.scrollBy(0, 95);
        await sleep(100);
    }
}
// Utils
function sleep(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
}PS. I'm not responsible if your accound get banned (Up until now, I wasn't banned) . Thanks!
You can check the "New to you" tab (make sure to scale the page to 80%)

I wonder what the consequences are for disliking videos instead of marking as not interesting, and if that would achieve a similar effect.