If you receive a reimbursement or refund in the same month as the original purchase:
Track it to the same line item where you recorded the original transaction. This will increase the available amount in the Remaining column for that line item, reflecting the money coming back.
If you receive a reimbursement or refund in a different month than the original purchase:
Record it as income under the Income group. This way, you can decide how to allocate that money anywhere in your budget, giving you more flexibility.