How can i avoid the permalink start with ‘blog’ while using the custom post type?

This can be set in a plugins’ options if you’re using a plugin to generate a Custom Post Type (such as CPT UI).

Otherwise if you’ve created this post type in the functions.php file you should amend or add to your your code as follows:

'with_front' => false

i.e. if your permalink structure appears as:

yourwebsite.co.uk/blog/custom-post-title

then setting this to ‘false’ will make your url something like:

yourwebsite.co.uk/custom-post-title