theme: Szeged - how to edit header

I am using RMarkdown Beamer and I set the theme: Szeged in the YAML header as per:

---
title: title

author: name
date: date

output:
  beamer_presentation:
    theme: Szeged
    slide_level: 2
    includes:
      in_header: header.tex
      
linkcolor: blue
---

header.tex

% remove title slides at beginning of sections
AtBeginSection{}
% add page counter to the footer
setbeamertemplate{footline}[frame number]

But I would like to remove the second section (between the 2nd and 3rd line) since I do not have anything there:

How can I do it?

Is it possible to change the colour of these lines as well?

% remove 2nd section from header
makeatletter
beamer@theme@subsectionfalse
makeatother
% change colour of lines
definecolor{mycolor}{RGB}{7,75,164}
setbeamercolor{separation line}{bg=mycolor}