If you’ve assembled your bike and the handlebars still feel loose, please do not ride the bike until the adjustment is corrected. Scroll down to *Section 8* of the following how-to guide for some tips and tricks on adjusting a threadless headset:
https://www.parktool.com/blog/repair-help/threadless-headset-service
First - loosen the side hardware holding the stem
Second - tighten the top cap bolt on top of the stem, you want this snug
Third - align the handlebars with your front wheel and tighten the side bolts of the stem
If you are still having trouble, please use the contact us page and send a quick email with a description of your issue, and we’ll reach out ASAP and provide additional instructions or connect with a local bicycle shop to get this adjustment made.