Re-importing the spreadsheet isn't going to work as it will skip any review that it finds in the review list already. You could perhaps delete all of them and then re-import, but that could risky. You could try on just a couple first. The best way to add a lot of tags are once is with the Bulk Edit button on the Review List page. It will add tags to all reviews currently filtered. 

I think I have this fixed in the Beta version 12.4.2 of the plugin. Can you give it a try? Just go to the Account page inside the plugin and check the "Join the Beta program" check box. Then the beta version should show up on the Updates page in WordPress. After you install the update. Deactivate and re-activate the plugin. That should force all the database table to update.

Are they showing as broken in the Review List?

This may be a question for Complianz customer support. I don't have a copy of that plugin to do any sort of testing.

You can use the CSS code. Just modify as you need and add it to the custom CSS code for the review template on the first tab.

span.wprev_totrevs {
font-size: 14px !important;
color: black;
}

Are you using the Advanced slider or the Normal? You can right-click on the arrow > inspect > and then it should show you what CSS classes are being used.

Once you have the CSS class you can overwrite it in the Custom CSS section of the review template like so...

.wprs_unslider-arrow {
width: 15px;
height: 15px;
}