Here's how to enable Multicurrency in QuickBooks Online:
How to enable Multi Currency
Step 1: Log in to your QBO Account and click on the gear icon in the upper right hand corner.
Step 2: Select Account and Settings.
Step 3: Click on Advanced
Step 4: Scroll down to the Currency section and click the pencil icon.
Step 5: Check the box for Multicurrency and the I understand I can't undo Multicurrency box. Click save.