It's recommended to have both of the records pulled up in separate GMSNext tabs so you can have quick access to both records. 

Navigate to the donor record where you are needing to move the transaction from. 

Find the transaction that you're needing to move and select it. 

Navigate to the Donor record that you're wanting the transaction to move to in your other GMSNext tab. 

Copy that Donor ID of the record where you're wanting to move the transaction. 

Back on the transaction record, input the Donor ID from the donor profile that you're wanting the transaction to move to. 

The transaction has now been moved to the new donor profile! 

Idonate

Use the following article to complete requested transaction moves from one donor record to another in GMSNext. 

How to Move Transactions from one donor account to another