Your domain is typically hosted by the company through which you purchased or registered the domain.
If you don’t recall where you registered your domain, a good place to start is to ask your current website provider if they have it. Often times the website provider will purchase it on your behalf.
You can also search your domain using this website: https://www.whois.com
If the provider that comes up rings a bell, contact their Support & ask for a password recovery.
Let us know if you need any assistance!