Redeemed Gift Card to my Microsoft account by accident

Hello, sorry its no way to transfer that balance to a different account. Only option would be if you find something you want and buy it as a gift and send it to correct account, if it allows you to use balance as payment.

I have tried to buy another gift card using my Microsoft account balance as payment method however it tells me 'Not available for purchase'.

How do I redeem my points to "gift" a gift card to be used by someone else on their own Microsoft account?

How to redeem a gift card or code online

The easiest way to redeem a gift card or code is online. Sign in to microsoft.com/redeem with your Microsoft
account, enter the 25-character code, and then select Next.

https://support.microsoft.com/en-us/help/10604/microsoft-account-redeem-gift-card-or-code

If you redeemed your rewards points for a Microsoft gift card or Xbox gift card, the balance should automatically be added to the account balance for the account that redeemed the points. They don't send you a code typically.