You've got my back, janaka-champitso. I can help you with changing multi-currency.
The Multi-currency feature is only available for QuickBooks Online Essentials, Plus, and Advanced. You can change the default currency on the Advanced page. I'll show you how:
Please note that once multi-currency is turned on, you're unable to turn it off. This is to avoid messing up the account, especially adjusting the sales tax.
Here are resources to learn more information about multi-currency and how it works in QBO:
Please let me know if I can be of any additional assistance. I'm always here to help.
If you are using QBO Global version, the multi currency feature is available on Essential and Plus plan. If you just open a QBO Simple Start account, you should open a new blank QBO account to get the discounted rate for 3 months. The rate is not applicable when upgrading your plan.