How do i use money from a different account for another?

Microsoft account balance cannot be transferred from one Microsoft account to another, and Microsoft personal accounts cannot be linked, merged, or combined.

What can still work in this case:

1. If the £5 was added as account balance on the Microsoft account, it stays on that account.
2. To buy something that costs more than £5, add another payment method on that same Microsoft account. During checkout, Microsoft uses the account balance first, then charges the rest to the other payment method.
3. If the reward had been kept as an unredeemed code, it could be redeemed on a different Microsoft account. But once redeemed, the balance belongs only to the account that redeemed it.

If the goal is to use one sign-in for purchases going forward, the practical option is to choose one Microsoft account and keep using that account for future redemptions and purchases.

• Microsoft gift cards terms and conditions | Microsoft Support
• Combining Microsoft accounts | Microsoft Support
• How to spend all of your Microsoft gift card money | Microsoft Support
• Can different accounts get stacked together - Microsoft Q&A