Hello Phiewefou16
First of all: good day and welcome.
This is not possible if you purchase the tickets in two single transactions as it is not possible to manually pick the seats. If you purchase the tickets together, the system will allocate the seats together.
Normally, a seat reservation is not necessary for that journey.
https://community.sbb-tickets.cc/d/23887-demystifying-seat-reservations-on-swiss-trains-a-comprehensive-guide
Please call SBB if you want to be reseated: +41 51 225 56 78 (24/7, waiting times are possible).
Btw, what is a txt? Text? I only knew ‘tkt’ or ‘tix’, for ticket.
Kind regards,
Roland