Lourdes Shrine destination

Looks like the only airline flying directly between Paris and Lourdes is Volutea, a European short haul budget airline flying out of Orly. But I think they only have a couple of early morning flights. If you want to do that on the same day you arrive in Paris, you'd either need to take a flight with connections, or take a train leaving late morning/early afternoon from Gare Montparnasse.

Which San Sebastian?

I think you'd have better luck taking train from Paris to Lourdes. From Lourdes, you can take the train (you'll need to switch at Hendaye I believe) to San Sebastian. You can confirm the train info on the official SNCF web site or on the app.

As Cjean pointed out, the only airline operating between Paris (Orly Airport) and Lourdes is Volotea, a Spanish "low-cost" airline with 2 flights per day.
But as it is unlikely that you will be able to catch the morning flight around 8:30, you will have to wait for the evening flight around 9:00 PM

See Volotea: https://www.volotea.com/en/

The other possible option is to fly from CDG to Toulouse with Air France (6 to 10 flights per day) and then take a direct train Toulouse→Lourdes (about 2 hours by train).
It is about 25 minutes by taxi or bus to go from Toulouse airport to the train station.

By train the journey CDG airport→Lourdes via Bordeaux is about 6h30, it is the simplest, easiest, and cheapest solution provided that a train departure matches your schedule. But you will still have to wait a few months before SNCF publishes the train schedules.

As specified above, you have to go through Hendaye to go to San Sebastian from Lourdes

I have to be at Lourdes before 4 pm on Sunday 7/13 to check in for service. I was hoping to get in early Sunday and catch a connecting flight in CDG and not to have to go to Orly.

Sorry I didn’t know there was another San Sebastián in Spain. I want to go to the one close to Lourdes. Thank you all for the feedback I will review all and decide how to proceed.

I think you would be struggling to arrive at Paris on the same day as your 4pm due reporting for service at Lourdes-

Working it backwards-

Trains Toulouse to Lourdes are currently at 1333, arrive 1522 (no room for any delay),
or
1133, arrive 1322

Say 1 hour to transfer from Toulouse airport to rail station that needs a flight arrival by 1030, thus leaving Paris by 0930.

That in turn needs an on time arrival at CDG no later than about 7am.

In short, even if you find such a flight a lot of parts have to go like clockwork, too many for my personal preferences.

I think that you need to be arriving at Paris the previous day, get to Toulouse that day, find an inexpensive hotel (at the airport if need be) then a mid morning train (even the 1133) on the Sunday morning.

Sorry I didn’t know there was another San Sebastián in Spain. I want
to go to the one close to Lourdes.

There is no other San Sebastian in Spain, we are talking about the same city, the one that is about 200km west of Lourdes, not far from the border with France. It is also called Donostia in Basque, once in Spain you will see both versions on all the signs.

I don’t want to be pessimistic but I don’t think you will be able to be in Lourdes at 4pm if you don’t arrive in France at least the day before.
So I would choose a safe solution, that of getting as close as possible to Lourdes the day before by flying from CDG to Toulouse as isn31 suggests and spending the night in Toulouse center before taking a train to Lourdes the following morning.