how do I request my refund to be transferred to next year's tax liability. Where is the input for box 894? I need to input a 2.

Are you preparing a personal (T1) or corporate (T2) return?

2024 T1.

Line 894 is only on the T2 return for corporations. On a T1 return in TurboTax Online, you'll be asked if you want to transfer your refund to your Instalment account just before you NETFILE your return.