I switched from LastPass to another password manager because LastPass has just a terrible UX. I wanted to delete all the entries from LastPass. But I couldn't find a way to do that. I contacted support and they confirmed there is no way to accomplish this. Of course there isn't.
They suggested I visit my vault and click every checkbox - all ~700 of them - and then click delete. So this simple Javascript in the console did it for me:
for (const c of document.getElementsByClassName('itemCheckbox')) {
c.click()
}
(that checkbox is actually a button which is why it needs a .click())
After Javascript selected all the items I just clicked the Actions -> Delete Selected and deleted them.
Maybe that'll help you too.