It depends. If someone had said they were interested before but you had a partner then, and gave that as a reason, then you could say something like “when you told me you were interested before, I had a partner and didn’t want to be disloyal, but that hasn’t worked out. It’s over. So if you are still interested we can go out”.
But if you are simply asking out of vanity then I don’t think it would be very nice to get the other person’s hopes up only to dash them again.
The golden meanie
In between those two extremes there lie all kinds of other scenarios, but I wouldn’t ask that person unless you are ready to go if they say “yes” and if you have a reasonable reason why you didn’t say yes before, such as that you had a partner then, or you were dealing with a stupid infatuation, or that you didn’t realise you has so much in common with the person. Or you thought they miht have been just joking around and now you hear they have a serious character and were probably not. Or you thought they were not going to be living in the area for long, or you weren’t going to be, and that’s changed. These are all reasonably valid reasons for changing your mind about someone’s approach.
“I said no earlier because I thought I had a chance with someone better than you” is a bad reason. I wouldn’t bother asking in those circs. Or “I didn’t know you were rich” is another bad reason.
Maybe the first step is to be honest with yourself as to what reason or reasons made you turn this person down before and what really changed. Then you can see if you can sell that reason to the other person.