I can’t log in to `wp-admin` after changing my domain

I created a website using wordpress. I decided to change my domain and bought it using the website: https://www.aftermarket.pl/

After buying a domain in the wordpress panel, I took the following steps:

1. Log in to WordPress
2. Click on the Settings menu.
3. Select General.
4. Update these fields with the new domain name:
5. Click Save Changes.

after following these steps I cannot log in to wp-admin. Entering through the old domain – oldsite.com redirects me to newsite.com where I can only see File not found.