How can I use two currency with quickbooks online ?

You'll need to activate the multicurrency feature in QuickBooks Online (QBO), @aggrey-ochieng-o. This way, you can use two currencies and tracks your foreign transactions. I'm here to guide you how.

The multicurrency feature gives you the ability to record your customers, suppliers, or bank accounts that use a currency other than the one you're using locally. It also lets you monitor your exchange rate gains and losses. Please note that once you turn the said feature on you can't turn it off again. Then, your home currency is set and can't be changed. It's also currently available in the Essentials and Plus versions of QBO.

Once ready, here are the steps:

1. Go to the Gear icon.
2. Select Account and settings.
3. Go to the Advanced menu.
4. Click anywhere in the Currency section to view its contents.
5. Choose your Home Currency.
6. Toggle Multicurrency on.
7. Confirm that you understand that you can't undo this option.
8. Click Save.

I've attached screenshots below for your reference.

After activating, you can assign a foreign currency to your customer. This is only applicable when they use one that's different from the one you're using. Then record transactions in the currency they pay you with. For the detailed steps, kindly check out this article: Assign a foreign currency to a customer in QuickBooks Online. It also contains instructions about changing the currency for an existing customer.

To monitor all your foreign transactions, you can pull up  the Realised and Unrealised Exchange Gains & Losses reports. Just go to the Standard tab's Business overview section from the Reports menu.

Please let me know if you have other concerns. I'm just around to help. Take care always.