Alright. So it's pretty straightforward. Note that you need to do all of these steps from your Kiwi Browser or it won't work. So this is for the add on by @interactivefics but it the same for any add ons you wanna add to Kiwi.

1. Open your three dot menu on the top left and click on extension.

You will find something looking like this

If you have no extension yet you only have the text at the end.

2. Click the Google hyperlink then the first link on the webpage. It should be like this

3. From that store, it will look like you're on desktop that's normal, select any add on you want to add to your phone. Please be aware some will instal but not work. You'll note I have an AO3 add on installed that I should really delete because it does not work on phone (but it works on computer). Interactive fics should however, I've used it. In fact I switched to Kiwi so I could use that add on specifically. But that might depend on the phone.

For the picture I choose to install Grammarly

4. Click on "install to Chrome"

5. Your phone will download a .crx file. It might take a couple of seconds. You will get a message the installation failed that is Normal!! It's trying to install a chrome file on a non chrome thing it doesn't get it.

6. Once you see this message, go back on the 3 dot menue then extension. Your extension should have installed even with the failed message

7. Open any new webpage on your phone, here I assume AO3 for fics but it can work on any page.

8. Open the 3 dots menu and scroll the menu all the way to the end to find your extension

9. Click on Interactive fics and change whatever you want (do this when you're on the right page to change)

And voilà!

Please be aware some add ons can work and other might not. That depends on the phone. This particular add on doesn't have cloud save so the first time you will have to re enter all your saved replacements but they should stay saved on your phone.