When my husband was showing signs of dementia, he was in total denial that there was a problem and blamed everything on me . It was extremely unpleasant.
Our GP has known us for years so I had a very good conversation with him where he thought that if he challenged my husband to agree to an assessment, just to prove that I was the one in the wrong, that there was nothing wrong with him, that he might go for it.
He was so convinced that I was the one who had the problem that he thought it was a great idea. But following the referral from the GP, nothing happened in a hurry so you need to be patient. There are scans, neuropsychological tests and other stuff that will happen and that will take months.
I don’t know if this could work for you but it did for me.