How do I isolate in Paris if I test positive for Covid?

You find a place to stay and order food in, etc. That means that you extend your stay at the hotel or find another one. A friend's son tested positive a day or so before his scheduled return. He extended his time in the apartment where he was staying and had groceries delivered. etc. The French authorities do not provide or pay for quarantine or isolation accommodation.

It's smart to think about these things ahead of time, so on the off chance it happens to you, you'll still be shocked at first, but then have an idea of what to do.

Before you leave home, I would contact the accommodations where you expect to be when you test. The hotel in Reims right before the tour, or Paris? Ask them if they could accommodate you for whatever the local requirement is for isolation. They may not know, but could perhaps give you an idea. When we did the Best of Spain in the spring we still had to test get to come home. We returned to Madrid to fly home and I had booked us in a hotel that Rick Steves uses. I called with the question a month or two ahead of time and they said they would accommodate us. Lo and behold, I tested positive, and they put us up for the 10 extra days we had to stay. You can check Booking.com ahead of time to get an idea of other options.

If you do test positive, you would have to let your tour guide know, and they would probably refer you to Travel Guard. There is information about their services under the "Documents" tab in your Tour Account so you can familiarize yourself with that information.

Spain does not have rigid isolation requirements, so, being very cautious and wearing masks everywhere, we were able to get our for walks once a day, and eat at outdoor cafes, so food was not really an issue for us. But I had made note of food delivery options before we left, and our hotel had a restaurant with room service.

There are other threads about this, but the main thing is to give it thought and have some ideas, so if it happens you don't feel totally at a loss.

It is hard to judge "tone" on a post but I am wondering if you are thinking that there is a specific facility that you go to to do your "isolation time"? In France, that has never been the case, you just isolated wherever you could find a hotel/apartment. If you are doing a self test you are not under an obligation to report to a health authority as far as I know so there is no governmental oversight now on your isolation period.

Here is the link to the French requirements if you test positive. I can only find this in French, not the English version. But you can use google translate to read the whole page.

https://www.gouvernement.fr/actualite/les-nouvelles-regles-d-isolement-et-de-quarantaine-face-au-covid-19

A little of the text translated says:

"For positive people with a complete and up-to-date vaccination schedule and for children under 12 years of age: isolation is for a period of 7 (full) days from the date of onset of symptoms or date of collection of the positive test.
However, after 5 days, the positive person can leave isolation on two conditions:
She performs an antigen or RT-PCR test and it is negative;
She has had no clinical signs of SARS-CoV-2 infection for 48 hours.
If the test carried out is positive or if the person does not carry out a test, his isolation is maintained at 7 days. She does not carry out a second test on D7."

So, if you are not symptomatic after days you can leave isolation. As mentioned this is not regulated by authorities any more as far as I can tell (if one of the folks in France gives a different answer go with theirs!).

This is not going to be a problem unless you have to return home to work by a certain time!