I want to update the confirmation form for delete user.

If user has posts, it shows Attribute all content to – option to reassign other author for his posts.
It takes lots-of time to load the page, if there are thousands of users in the system. (we have 55k+ users)

So, I want to change the User option (Attribute all content to) from Drop-down to Type and Search.

I’ve tried to found the hooks/action but could not found that I want. I don’t want to update wordpress core files to change this.

Please suggest me hooks/action for my question.

Thanks.