use a humidifier during the vegetative stage, if humidity rises too much you can counteract it with an air intake or fan, during this stage try to keep humidity as close to 60% with a temperature of 24 to 26 degrees Celsius, for the flowering stage you won't need a humidifier anymore, in that stage I recommend lowering humidity to 40% or maybe even 30%
if you don't have a humidifier I recommend misting the seedling with a spray bottle whenever humidity drops 😃, if you have any questions feel free to ask.
Good luck!