On the tour page, there is a "Members" section - you need to sign up for that if you want to buy Presale Tickets! It takes 15 seconds.
People also said you need to sign up for Crowdsurge, but I'm not 100% sure on that. I signed up anyway just in case. The Members section seems to be powered by Crowdsurge, so maybe that's what they meant. Both are free to sign up for, so it doesn't hurt I guess.
When you sign up for the Members section on weirdal.com, you get a message that says:
How cool is that??You’ve been entered for a chance to win an exclusive signed Vinyl LP of "Mandatory Fun!" You’ll also receive early access to pre-sale tickets, content and more.
Again, just a PSA - not sure if this was already known or not.