Hello @Surine0,
For each room that you want to rent separately, go through the same process that you've already done for the house.
Go to "Host", "Manage listings" and then click on "Add new listing". Set the listing as being a shared room. Give a price, say whether it's a shared bathroom or private, say which amenities it has, is the kitchen / living room shared, house rules, etc.
If you also want to be able to rent all four rooms to larger groups then keep your current listing.
Remember that if you receive a booking for one of the rooms then you'll have to block those dates on the calendar for the four room listing and vice versa. If you do keep the four room listing then, to avoid double booking, it's best not to have instant book for any of the listings.
Steve.