<p>1 - Lorem, ipsum dolor.</p>
<p>2 – Lorem, ipsum dolor.</p>
<p>3 — Lorem, ipsum dolor.</p>
<p>4 - Lorem, ipsum dolor.</p>
<p>5 – Lorem, ipsum dolor.</p>
<p>6 — Lorem, ipsum dolor.</p>
<button type="button">Найти и заменить</button>

p {
    margin: 10px;
    font-family: sans-serif;
}

button {
    margin: 10px;
}

const button = document.querySelector('button');

button.addEventListener('click', event => {
    const walker = document.createTreeWalker(document.body, NodeFilter.SHOW_TEXT);
    const expression = /[-–—]/g;

    while (walker.nextNode()) {
      const node = walker.currentNode;

      if (expression.test(node.textContent)) {
        node.textContent = node.textContent.replace(expression, '-');
      }
    }
});