Hi, today’s direct-drive trainers will not work with bikes with less than 8 speeds on the cassette. A better route in your case is to use a trainer where you leave the rear wheel on the bike.
Two reasons for direct drive trainers being a poor choice in your instance:
A. The spacing of your frame at 126 mm is too tight to fit on the trainer’s axle, which is 130mm at its narrowest configuration. 4 mm doesn’t sound like much, but you do not want to stretch the frame apart and start wailing on the pedals. That frame will eventually crack from those stresses.
B. A 6 speed cassette will not fit on modern freehub bodies, such as the one on your trainer.