What would you like to book ?

b-europe doesn't work for Interrail/Eurail reservations directly. You have to use this link for TGVs within France (to Strasbourg or Mulhouse on your itinerary) : https://travel.b-europe.com/Eurail-GE/en/booking-tgv#TravelWish

I thought that you had already booked the TGV ?

Strasbourg/Mulhouse - Basel - Visp - Zermatt cannot be booked. Simply add the train to Rail Planner app before boarding, you get a QR-code which is your ticket and that's it You can sit wherever you want on the train. This is the same process for the vast majority of European trains.

So I've seen your other post :

I wouldn't recommend to cancel last-minute. Trains are almost full (if not full) so you surely won't all sit in the same carriage or even on the same train. The connection with 2 changes is by taking the TGV to Basel directly : it has an expensive seat reservation fee of 37€ 2nd class/70€ 1st class. That's why we advised you not to take it. Changing in Mulhouse will be fine and there are trains every 30 min onwards so it's not a big deal if you were to miss one (no seat reservations required at any point).

I was trying to get earlier timed tickets and 1st class seats instead of 2nd class since we paid lots for eurail 1st class

Yes but you’d have had to pay 70€ per person to win 30 min. Really not worth the expense : it is the most expensive journey for 1st class passholders.

Are you on the TGV to Mulhouse now at 300 km/h ? Don’t worry about the connections frankly. And train journeys are fully part of the trip ! :)