Finally I found a solution on how to unretweet properly on Twitter. Therefore below I list it into a few steps in case I need to do this kind of thing again in the future.
[ STEP 1 ] - Find the tweet ID you want to unretweet, for example
[ STEP 2 ] - Remember the numbers
1140605960387534849, copy it to somewhere else, because you need to use in the next step.
[ STEP 3 ] - Open Google Chrome or any Chromium based browser.
[ STEP 4 ] - When you are inside twitter.com, open your console or press [ Ctrl ] + [ Shift ] + [ J ].
[ STEP 5 ] - Then click on the
Network tab, then find the word
Fetch/XHR and click on it.
[ STEP 6 ] - While the console is still open, switch your focus back to twitter.com, just try to find any tweet available on your eyes, then retweet that tweet, and then unretweet that tweet.
[ STEP 7 ] - Now switch your focus back to the console, the
network tab, check on the log, under the name section, find
unretweet.json which has the type
xhr, then right click on it, then click
Copy, then click
Copy as fetch
[ STEP 8 ] - Then focus your eyes above the menu, find the word
Console, then click on the word
[ STEP 9 ] - Now while you are in Console, there is a sign
>, then [ Mouse Right Button Click ], then hover to the word
Paste, then [ Mouse Left Button Click ], or you can also press on your keyboard [ Ctrl ] + [ V ]
[ STEP 10 ] - You can skip this step if you only want to unretweet just one retweet, if there are a lot of of retweet you want to unretweet, press on your keyboard [ Ctrl ] + [ V ] into any text editor because you need to use this text again and again in the future
[ STEP 11 ] - Then on text you just pasted on the console, try to find the word
"body": "tweet_mode=extended&id=, after that replace whatever number shown there with the tweet ID you want to unretweet, in this case
[ STEP 12 ] - Then press [ Enter ] on your keyboard.
[ STEP 13 ] - Open another tab, or another window referring to your own twitter.com username, first you must log off so that you can properly see what others can see but you cannot see while you are still logged in your Twitter account, then check whether you successfully unretweet the tweet you want to unretweet, press [ Ctrl ] + [ R ] to refresh the web page and see the result.
[ STEP 14 ] - If there are too many retweet you want to unretweet, then hover your mouse to the first line of text you copied from the network tab before, before the word
fetch, before the alphabet
f, then [ Mouse Left Button Click ] on that area, check if there is something blinking on and off first, then switch your focus to your keyboard, then press [ Shift ] + [ ↓ ] until the end of the text shown, in this case
});, if the text is not visible on your eyes, then while holding your mouse, drag the scroller on your mouse [ Mouse Scroll Down ], you can also just press [ Ctrl ] + [ C ] after highlighting all the text you copied and paste before in [ STEP 10 ] and paste it on the next line in your console, by pressing [ Ctrl ] + [ V ] on your keyboard
[ STEP 15 ] - When you can see the symbol
> in black colour is visible on your eyes with white space on the right of its side, then press [ Ctrl ] + [ V ] on your keyboard.
[ STEP 16 ] - Repeat the step from [ STEP 1 ] to [ STEP 12 ] using different tweet ID
[ STEP 17 ] - DONE