At one time, you can set prices for rooms of identical capacity (number of people).
How to set prices for rooms of different capacity (number of people)?
If you have rooms for two and three guests, then:
a) first set prices for double rooms (on the price grid, click on any of the double rooms and then in the "Set prices" window use the "Select rooms with the same capacity" option);
b) then set prices for three-person rooms (on the price grid, click on any of the three-person rooms and then in the "Set prices" window use the "Select rooms with the same capacity" option).