Oh the shame! I’m so sorry for missing this message! :(

When editing or creating a post you’ll see several buttons above the area where you write your post. Between the “b-quote” (for quotes) and the “img” (for images) button, you’ll see a button which says “del” and this word is crossed out. Select the text you want to have crossed out, and then click this button! And that’s it!

Hope this helps you :)