Since you're asking this question in most cases I would respond with... just talk to your web host and domain registrar since your paying for a service and therefore they should offer you support and provide the 'exact' information, from where to click and what to input.
But if you want to get hands-on or learn a little then...
Currently, it sounds like you're pointing your domain to another party's nameserver, what this essentially means is the domain configuration file AKA Zone File is held with the 3rd party and therefore you need to update that file which is normally done by some type of dashboard.
If using cPanel/Plesk website hosting then you may be able to update the zone file via the cPanel or Plesk dashboard, but most shared hosting providers disable this option and therefore you would be required to contact your website host.
Alternatively, you can reset the nameservers back to your domain registrar and then point the A record & MX records to your website host and then setup a CNAME pointing to Blogger.