Scroll down towards the bottom and click the Change Country link (see image below.)
Hit United States. Then, scroll up and tick the Plans & Pricing tab at the top.
Enable the switch button for Free trial for 30 days. You can use the same user ID and password with your existing account.
Choose your plan and then pick Select.
Follow the next steps that'll guide you through the rest.
Once you're done, you can import your data from your existing account. Need details? Check out this guide: Move your lists to QuickBooks Online.
In case you need help with other QBO tasks, click this link to guide you with your first hour in QuickBooks.
Keep me posted if you still have questions. Just drop them in the reply section below and I'll be happy to answer them for you. Have a lovely day ahead.
As an additional info, If you have to open a new QBO account, make sure to click the Buy button to get the discounted price for up to 3 or 6 months. If you purchase from the Trial account, you have to pay the regular rate.