If you are saying you now need Financial POA, that isn't possible unless your Uncle can participate. If your Uncle becomes able to participate you can have a Lawyer come with the papers done, and the Uncle can sign. You would not be able to be present when Lawyer interviewed the Uncle for competency. IF you are unable to have now a way to help handle the Uncle's finances and there is a critical need to do so now, then go to the Hospice Social Worker for assistance. She or he is a part of their team (or anyway that's how it once was). You may realistically not be able to handle this. In all truth there is really no way that Financial POA would help anything here; it disappears at death and his assets go to Will, Trust, or Probate with appointed executor. It would help if you tell us what you are trying to accomplish for him at this time.
I believe if you want to change your POA for him, he would have to be able to sign and know what he’s signing. We changed my husband’s POA rather easily, but we needed two witnesses and he was able to sign it. And, the new POA was drawn up by an attorney.
I faced the same situation with my dad. I aged 10 years during that wretched time.
Is there something specific that you need to handle? I might be able to help you, you can private message me if you are more comfortable with that.