Good Morning J3! Still learning about your airplane I see! Good.
You don't need autopilot to adjust trim speed. Go to Vans website, RV-12 plan revisions 2nd page, and get Page 45-08 Rev 2. It shows the back of the D-180 modules and explains how to adjust trim speed.
A word of caution. The trim pot is not mounted in a particulary friendly place and you need to be careful with your tiny little screwdriver, as mentioned in the plans. Good luck!