Easy, with regex search!

• Press Ctrl+R for show replace bar
• Enable regex mode (button looks like .* near search field)
• Use regex in search field: '(.+)'\s=>\s'(.+)',
• Use expression for replace: '$2' => '$1',

You can see a tooltip with a value that will be after replace

It is possible even you have different quotes and spaces between arrow

Use regex
(?:'|")(.+)(?:'|")\s{0,}=>\s{0,}(?:'|")(.+)(?:'|"),

And the same replace expression '$2' => '$1',

Named capture groups also available:

Use regex
(?:'|")(?<src>.+)(?:'|")\s{0,}=>\s{0,}(?:'|")(?<tgt>.+)(?:'|"),

And the same replace expression '${tgt}' => '${src}',