why exchange gain or loss not the same figures? as currency revaluation?

I understand why you're at a loss. These two figures measure different things, so they won't match. QuickBooks tracks exchange gains and losses on paid transactions for your profit and loss report, but it leaves open unpaid invoices or bills at their original recorded rate.
 

Your previous accountant likely looked only at settled items and missed your open balances. This left those exchange changes unrecorded, which caused the gap your new accountant found.
 

The revaluation tool fixes this by updating your open foreign currency balances at the year-end rate. This ensures your balance sheet reflects their true sterling value since QuickBooks doesn't run it automatically.
 

To fix the issue, your new accountant needs to go back to the affected years and run the revaluation with the correct dates. Moving forward, running it every year before pulling your final reports will keep everything accurate.
 

You can check this article for more details: Home currency adjustments in QuickBooks.
 

Feel free to reply if you have any other questions or concerns.