Thanks for the model. That's a pretty pricey Indian model!
https://www.reach2fitness.com/produc...icta-spin-bike. You might try their customer service, but I don't have much hope.
It looks like the mfr. doesn't post a link to the manual, sigh. It looks like it is electronically controlled, through a touchpad. From your description there aren't many levels -- maybe 10? Frankly, the Nordictrack's 24 levels makes the adjustment pretty fine-grained.
It is probably using the same control system as the Nordictrack bikes: an electric motor moves a magnet closer to the flywheel for more resistance. You could remove the covers to check. There will be a linkage that can be adjusted between the motor and the magnet. Here's a vid on the subject:
The other "fix" would be to use the trainer to work on your spin (cadence) while leaving the resistance @ 5 to get your heartrate up to where you want it. It won't be like riding outdoors, but that's what the outdoors is for. Real rides are a continuous succession of varying resistances, unlike the extremely uniform trainer. You could simulate that by switching resistance levels often.