If the intent is to move a request from one account to another, you will have to first move the requester to the correct account, and then you will be able to change the account in the requests.
1. Go to Admin - > Account details - > Requesters. Go to the requester (present in the requests) whose account has to be changed. Edit the requester, and change the Account using the drop-down as shown below, save the setting.
2. Go to request list view, select All accounts from the drop-down, and select the requests whose account has to be changed, click on Actions - > Edit, as shown below.
3. In the pop-up shown to edit, click on Site drop-down, and choose the correct Account and site, save the setting.
So, now, the selected requests' Account would have been changed.