When you create a Home currency adjustment, QuickBooks Online creates a journal entry with zero gain or loss for Accounts Receivable or Accounts Payable. The journal entries keep track of the date you revalued a currency, the currency you revalued, and the exchange rate.
Reports use the exchange rate from such adjustments to calculate unrealized gains and losses.
Home currency adjustment journal entries with non-zero dollar amounts indicate that you've run Home currency adjustments on bank or credit card accounts and have realized gains or losses.
While you can edit the journal entry's number and Memo field, and adda attachments for your records, you can't change the date, debit or credit amounts, or exchange rate for the journal entry to ensure that unrealized gain or loss amounts can be accurately calculated on reports.
If you need to change the date or the exchange rate, you'll have to delete the journal entry and run the currency revaluation again.