As long as you don't have eggs in the bator, why not see how high the humidity will go. At some point, at lockdown, you are going to have to raise the humidity to at least 60%. I'd let it go until it stabilizes & see what it is, then you know what to do at lockdown to get it up where you need it.
As long as it's empty you can just shut it off, empty out the water, dry it out & re-start it. Before you put eggs in you might want to only put in enough water to get the humidity to around 35-40% to start. I've seen the humidity raise after putting eggs in& you don't want it to high to begin with. You can always raise it to what ever you want after everything stabilizes
Don't know what kind of bator you are using, but isn't the vent supposed to be open?