Merging two Custom Post Types into one

I am new to all this so my ignorance may get in the way.

I inherited a WP Blog with Custom Post Types. There are 4 Custom Post Types, out of which 2, Books and Magazines, have the same fields: Custom_Post_Type_Name, Author, City, Address, Categories, Tags, Date.

I need to merge these two Custom Post Types into one. More specifically, I need to merge Books into Magazines and rename this new merged Custom Post Type to Publications.

Can someone please show me how to do this?

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