Good news that the hog house was being made use of during the winter.
There is some information about cleaning out hog boxes here: https://www.hedgehogstreet.org/cleaning-out-boxes/
Just make sure that there is no hog in residence. If there is leave it be and hope that it moves out soon.
Re. encouraging a female to nest there. Hogs are pretty much their own hogs and do their own thing, however much we might encourage or otherwise! But there is a chance that a female could use the hog house. It’s best after cleaning (make sure you use boiling water to kill any potential parasite eggs and well as generally cleaning out) to just put a small amount of bedding into the box and leave a selection of material nearby for the hog to take in itself. Many prefer to do their own interior decorations and a female might have her own ideas, especially if she is planning a birthing nest.
Good luck. I hope a female does decide to move in. It would be lovely to have hoglets in your garden.
Happy hog watching!