Hello i start my blog last year now i get huge traffic from all countries now i buyed a domain but i faced a problem i create backlinks with my blogspot link now if i add domain so i think i lost my traffic so any solution for that i use both links domain as well as blogspot.
You just need to set it up so that your old domain redirects to your new one, something you can easily do with Blogger. You won't get ALL of your link juice transferred, but you will get enough of it to keep your momentum...I hope that helps!
You can add the new domain at BlogSpot. Everytime people coming to your website using your old .blogspot URL, it'll show a notification telling your visitors that you've changed your domain. I don't think there's other way.
Yea what I'm saying is all of your old traffic should just be redirected to your new domain automatically. Maybe I'm misunderstanding you, sorry if that's the case.
redirecting traffic to your new domain name is probably the best way to deal with your situation. Hope i got you well